From 0939e1630bd1c834b48bf4075567424b271def43 Mon Sep 17 00:00:00 2001
From: "stevenjb@chromium.org"
 <stevenjb@chromium.org@0039d316-1c4b-4281-b951-d872f2087c98>
Date: Wed, 12 Mar 2014 19:35:36 +0000
Subject: [PATCH] Fix incorrect use of AppListItemList::FindItem

This CL should:
* Fix a Folders bugs where existing items in folders were not found (causing them not to be updated and potentially creating duplicate items)
* Protect the code against similar errors in the future
* Correctly protect against an edge case where multiple items might have the same ordianl

BUG=350165, 346117
For sync_app_list_helper.cc:

R=jennyz@chromium.org, tapted@chromium.org
TBR=zea@chromium.org

Review URL: https://codereview.chromium.org/190953012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256603 0039d316-1c4b-4281-b951-d872f2087c98
---
 .../test/integration/sync_app_list_helper.cc  |  65 ++++++-----
 .../browser/ui/app_list/extension_app_item.cc |  10 +-
 .../browser/ui/app_list/extension_app_item.h  |   5 +-
 .../app_list/extension_app_model_builder.cc   |  29 ++---
 .../extension_app_model_builder_unittest.cc   |   8 +-
 .../browser/ui/app_list/fast_show_pickler.cc  |  14 ++-
 .../test/fast_show_pickler_unittest.cc        |  21 ++--
 ui/app_list/app_list_folder_item.cc           |   5 +
 ui/app_list/app_list_folder_item.h            |   1 +
 ui/app_list/app_list_item.cc                  |   2 +
 ui/app_list/app_list_item.h                   |   4 +
 ui/app_list/app_list_item_list.cc             |  77 +++++++++----
 ui/app_list/app_list_item_list.h              |   6 +
 ui/app_list/app_list_item_list_observer.h     |   1 +
 ui/app_list/app_list_item_list_unittest.cc    | 109 +++++++++++++++---
 ui/app_list/app_list_model.cc                 |  52 +++++----
 ui/app_list/app_list_model.h                  |  29 +++--
 ui/app_list/app_list_model_unittest.cc        |  72 ++++++------
 ui/app_list/cocoa/apps_grid_controller.mm     |  11 +-
 .../cocoa/apps_grid_controller_unittest.mm    |  13 ++-
 ui/app_list/test/app_list_test_model.cc       |  18 +--
 ui/app_list/views/app_list_folder_view.cc     |   6 +-
 ui/app_list/views/app_list_folder_view.h      |  10 +-
 ui/app_list/views/app_list_main_view.cc       |   8 +-
 ui/app_list/views/apps_container_view.cc      |   2 +-
 ui/app_list/views/apps_grid_view_unittest.cc  |   8 +-
 26 files changed, 365 insertions(+), 221 deletions(-)

diff --git a/chrome/browser/sync/test/integration/sync_app_list_helper.cc b/chrome/browser/sync/test/integration/sync_app_list_helper.cc
index 79dc84e4ec07e6..ef862283ef8a6a 100644
--- a/chrome/browser/sync/test/integration/sync_app_list_helper.cc
+++ b/chrome/browser/sync/test/integration/sync_app_list_helper.cc
@@ -29,11 +29,9 @@ SyncAppListHelper* SyncAppListHelper::GetInstance() {
   return instance;
 }
 
-SyncAppListHelper::SyncAppListHelper() : test_(NULL), setup_completed_(false) {
-}
+SyncAppListHelper::SyncAppListHelper() : test_(NULL), setup_completed_(false) {}
 
-SyncAppListHelper::~SyncAppListHelper() {
-}
+SyncAppListHelper::~SyncAppListHelper() {}
 
 void SyncAppListHelper::SetupIfNecessary(SyncTest* test) {
   if (setup_completed_) {
@@ -43,11 +41,11 @@ void SyncAppListHelper::SetupIfNecessary(SyncTest* test) {
   test_ = test;
 
   for (int i = 0; i < test->num_clients(); ++i) {
-    extensions::ExtensionSystem::Get(
-        test_->GetProfile(i))->InitForRegularProfile(true);
+    extensions::ExtensionSystem::Get(test_->GetProfile(i))
+        ->InitForRegularProfile(true);
   }
-  extensions::ExtensionSystem::Get(
-      test_->verifier())->InitForRegularProfile(true);
+  extensions::ExtensionSystem::Get(test_->verifier())
+      ->InitForRegularProfile(true);
 
   setup_completed_ = true;
 }
@@ -59,32 +57,35 @@ bool SyncAppListHelper::AppListMatchesVerifier(Profile* profile) {
       AppListSyncableServiceFactory::GetForProfile(test_->verifier());
   // Note: sync item entries may not exist in verifier, but item lists should
   // match.
-  if (service->model()->item_list()->item_count() !=
-      verifier->model()->item_list()->item_count()) {
+  if (service->model()->top_level_item_list()->item_count() !=
+      verifier->model()->top_level_item_list()->item_count()) {
     LOG(ERROR) << "Model item count: "
-               << service->model()->item_list()->item_count()
-               << " != " << verifier->model()->item_list()->item_count();
+               << service->model()->top_level_item_list()->item_count()
+               << " != "
+               << verifier->model()->top_level_item_list()->item_count();
     return false;
   }
   bool res = true;
-  for (size_t i = 0; i < service->model()->item_list()->item_count(); ++i) {
-    AppListItem* item1 = service->model()->item_list()->item_at(i);
-    AppListItem* item2 = verifier->model()->item_list()->item_at(i);
+  for (size_t i = 0; i < service->model()->top_level_item_list()->item_count();
+       ++i) {
+    AppListItem* item1 = service->model()->top_level_item_list()->item_at(i);
+    AppListItem* item2 = verifier->model()->top_level_item_list()->item_at(i);
     if (item1->CompareForTest(item2))
       continue;
 
     LOG(ERROR) << "Item(" << i << "): " << item1->ToDebugString()
                << " != " << item2->ToDebugString();
     size_t index2;
-    if (!verifier->model()->item_list()->FindItemIndex(item1->id(), &index2)) {
+    if (!verifier->model()->top_level_item_list()->FindItemIndex(item1->id(),
+                                                                 &index2)) {
       LOG(ERROR) << " Item(" << i << "): " << item1->ToDebugString()
                  << " Not in verifier.";
     } else {
       LOG(ERROR) << " Item(" << i << "): " << item1->ToDebugString()
                  << " Has different verifier index: " << index2;
-      item2 = verifier->model()->item_list()->item_at(index2);
-      LOG(ERROR) << " Verifier Item(" << index2 << "): "
-                 << item2->ToDebugString();
+      item2 = verifier->model()->top_level_item_list()->item_at(index2);
+      LOG(ERROR) << " Verifier Item(" << index2
+                 << "): " << item2->ToDebugString();
     }
     res = false;
   }
@@ -118,7 +119,7 @@ bool SyncAppListHelper::AllProfilesHaveSameAppListAsVerifier() {
 void SyncAppListHelper::MoveApp(Profile* profile, size_t from, size_t to) {
   AppListSyncableService* service =
       AppListSyncableServiceFactory::GetForProfile(profile);
-  service->model()->item_list()->MoveItem(from, to);
+  service->model()->top_level_item_list()->MoveItem(from, to);
 }
 
 void SyncAppListHelper::MoveAppToFolder(Profile* profile,
@@ -127,7 +128,7 @@ void SyncAppListHelper::MoveAppToFolder(Profile* profile,
   AppListSyncableService* service =
       AppListSyncableServiceFactory::GetForProfile(profile);
   service->model()->MoveItemToFolder(
-      service->model()->item_list()->item_at(index), folder_id);
+      service->model()->top_level_item_list()->item_at(index), folder_id);
 }
 
 void SyncAppListHelper::MoveAppFromFolder(Profile* profile,
@@ -150,18 +151,18 @@ void SyncAppListHelper::CopyOrdinalsToVerifier(Profile* profile,
       AppListSyncableServiceFactory::GetForProfile(profile);
   AppListSyncableService* verifier =
       AppListSyncableServiceFactory::GetForProfile(test_->verifier());
-  verifier->model()->item_list()->SetItemPosition(
-      verifier->model()->item_list()->FindItem(id),
-      service->model()->item_list()->FindItem(id)->position());
+  verifier->model()->top_level_item_list()->SetItemPosition(
+      verifier->model()->FindItem(id),
+      service->model()->FindItem(id)->position());
 }
 
 void SyncAppListHelper::PrintAppList(Profile* profile) {
   AppListSyncableService* service =
       AppListSyncableServiceFactory::GetForProfile(profile);
-  for (size_t i = 0; i < service->model()->item_list()->item_count(); ++i) {
-    AppListItem* item = service->model()->item_list()->item_at(i);
-    std::string label =
-        base::StringPrintf("Item(%d): ", static_cast<int>(i));
+  for (size_t i = 0; i < service->model()->top_level_item_list()->item_count();
+       ++i) {
+    AppListItem* item = service->model()->top_level_item_list()->item_at(i);
+    std::string label = base::StringPrintf("Item(%d): ", static_cast<int>(i));
     PrintItem(profile, item, label);
   }
 }
@@ -183,8 +184,8 @@ void SyncAppListHelper::PrintItem(Profile* profile,
     }
     return;
   }
-  VLOG(1)
-      << label << item->ToDebugString()
-      << " Page: " << s->GetPageOrdinal(id).ToDebugString().substr(0, 8)
-      << " Item: " << s->GetAppLaunchOrdinal(id).ToDebugString().substr(0, 8);
+  VLOG(1) << label << item->ToDebugString()
+          << " Page: " << s->GetPageOrdinal(id).ToDebugString().substr(0, 8)
+          << " Item: "
+          << s->GetAppLaunchOrdinal(id).ToDebugString().substr(0, 8);
 }
diff --git a/chrome/browser/ui/app_list/extension_app_item.cc b/chrome/browser/ui/app_list/extension_app_item.cc
index 697e69c6fa25d7..7daa0506663247 100644
--- a/chrome/browser/ui/app_list/extension_app_item.cc
+++ b/chrome/browser/ui/app_list/extension_app_item.cc
@@ -203,11 +203,6 @@ void ExtensionAppItem::UpdateIcon() {
   SetIcon(icon, true);
 }
 
-void ExtensionAppItem::UpdateIconOverlay() {
-  if (has_overlay_ != NeedsOverlay())
-    UpdateIcon();
-}
-
 void ExtensionAppItem::Move(const ExtensionAppItem* prev,
                             const ExtensionAppItem* next) {
   if (!prev && !next)
@@ -335,6 +330,11 @@ ui::MenuModel* ExtensionAppItem::GetContextMenuModel() {
   return context_menu_->GetMenuModel();
 }
 
+void ExtensionAppItem::OnExtensionPreferenceChanged() {
+  if (has_overlay_ != NeedsOverlay())
+    UpdateIcon();
+}
+
 // static
 const char ExtensionAppItem::kItemType[] = "ExtensionAppItem";
 
diff --git a/chrome/browser/ui/app_list/extension_app_item.h b/chrome/browser/ui/app_list/extension_app_item.h
index be256830f9bd77..f52e1273a7a1d5 100644
--- a/chrome/browser/ui/app_list/extension_app_item.h
+++ b/chrome/browser/ui/app_list/extension_app_item.h
@@ -51,9 +51,6 @@ class ExtensionAppItem : public app_list::AppListItem,
   // it gray.
   void UpdateIcon();
 
-  // Only updates the icon if the overlay needs to be added/removed.
-  void UpdateIconOverlay();
-
   // Update page and app launcher ordinals to put the app in between |prev| and
   // |next|. Note that |prev| and |next| could be NULL when the app is put at
   // the beginning or at the end.
@@ -92,6 +89,8 @@ class ExtensionAppItem : public app_list::AppListItem,
   // Overridden from AppListItem:
   virtual void Activate(int event_flags) OVERRIDE;
   virtual ui::MenuModel* GetContextMenuModel() OVERRIDE;
+  // Updates the icon if the overlay needs to be added/removed.
+  virtual void OnExtensionPreferenceChanged() OVERRIDE;
   virtual const char* GetItemType() const OVERRIDE;
 
   // Overridden from app_list::AppContextMenuDelegate:
diff --git a/chrome/browser/ui/app_list/extension_app_model_builder.cc b/chrome/browser/ui/app_list/extension_app_model_builder.cc
index da1fc5da32bc0a..13acfef0d3da7d 100644
--- a/chrome/browser/ui/app_list/extension_app_model_builder.cc
+++ b/chrome/browser/ui/app_list/extension_app_model_builder.cc
@@ -59,14 +59,14 @@ ExtensionAppModelBuilder::ExtensionAppModelBuilder(
 
 ExtensionAppModelBuilder::~ExtensionAppModelBuilder() {
   OnShutdown();
-  model_->item_list()->RemoveObserver(this);
+  if (!service_)
+    model_->top_level_item_list()->RemoveObserver(this);
 }
 
 void ExtensionAppModelBuilder::InitializeWithService(
     app_list::AppListSyncableService* service) {
   DCHECK(!service_ && !profile_);
   model_ = service->model();
-  model_->item_list()->AddObserver(this);
   service_ = service;
   profile_ = service->profile();
   InitializePrefChangeRegistrar();
@@ -79,7 +79,7 @@ void ExtensionAppModelBuilder::InitializeWithProfile(
     app_list::AppListModel* model) {
   DCHECK(!service_ && !profile_);
   model_ = model;
-  model_->item_list()->AddObserver(this);
+  model_->top_level_item_list()->AddObserver(this);
   profile_ = profile;
   InitializePrefChangeRegistrar();
 
@@ -91,6 +91,8 @@ void ExtensionAppModelBuilder::InitializePrefChangeRegistrar() {
           switches::kEnableStreamlinedHostedApps))
     return;
 
+  // TODO(calamity): analyze the performance impact of doing this every
+  // extension pref change.
   extensions::ExtensionsBrowserClient* client =
       extensions::ExtensionsBrowserClient::Get();
   extension_pref_change_registrar_.Init(
@@ -102,16 +104,7 @@ void ExtensionAppModelBuilder::InitializePrefChangeRegistrar() {
 }
 
 void ExtensionAppModelBuilder::OnExtensionPreferenceChanged() {
-  // TODO(calamity): analyze the performance impact of doing this every
-  // extension pref change.
-  app_list::AppListItemList* item_list = model_->item_list();
-  for (size_t i = 0; i < item_list->item_count(); ++i) {
-    app_list::AppListItem* item = item_list->item_at(i);
-    if (item->GetItemType() != ExtensionAppItem::kItemType)
-      continue;
-
-    static_cast<ExtensionAppItem*>(item)->UpdateIconOverlay();
-  }
+  model_->NotifyExtensionPreferenceChanged();
 }
 
 void ExtensionAppModelBuilder::OnBeginExtensionInstall(
@@ -262,8 +255,7 @@ void ExtensionAppModelBuilder::SetHighlightedApp(
 
 ExtensionAppItem* ExtensionAppModelBuilder::GetExtensionAppItem(
     const std::string& extension_id) {
-  app_list::AppListItem* item =
-      model_->item_list()->FindItem(extension_id);
+  app_list::AppListItem* item = model_->FindItem(extension_id);
   LOG_IF(ERROR, item &&
          item->GetItemType() != ExtensionAppItem::kItemType)
       << "App Item matching id: " << extension_id
@@ -285,15 +277,14 @@ void ExtensionAppModelBuilder::UpdateHighlight() {
 void ExtensionAppModelBuilder::OnListItemMoved(size_t from_index,
                                                size_t to_index,
                                                app_list::AppListItem* item) {
+  DCHECK(!service_);
+
   // This will get called from AppListItemList::ListItemMoved after
   // set_position is called for the item.
-  app_list::AppListItemList* item_list = model_->item_list();
   if (item->GetItemType() != ExtensionAppItem::kItemType)
     return;
 
-  if (service_)
-    return;
-
+  app_list::AppListItemList* item_list = model_->top_level_item_list();
   ExtensionAppItem* prev = NULL;
   for (size_t idx = to_index; idx > 0; --idx) {
     app_list::AppListItem* item = item_list->item_at(idx - 1);
diff --git a/chrome/browser/ui/app_list/extension_app_model_builder_unittest.cc b/chrome/browser/ui/app_list/extension_app_model_builder_unittest.cc
index 870e52ebe2293e..e55327b4719793 100644
--- a/chrome/browser/ui/app_list/extension_app_model_builder_unittest.cc
+++ b/chrome/browser/ui/app_list/extension_app_model_builder_unittest.cc
@@ -35,10 +35,10 @@ const char kPackagedApp2Id[] = "jlklkagmeajbjiobondfhiekepofmljl";
 // Get a string of all apps in |model| joined with ','.
 std::string GetModelContent(app_list::AppListModel* model) {
   std::string content;
-  for (size_t i = 0; i < model->item_list()->item_count(); ++i) {
+  for (size_t i = 0; i < model->top_level_item_list()->item_count(); ++i) {
     if (i > 0)
       content += ',';
-    content += model->item_list()->item_at(i)->name();
+    content += model->top_level_item_list()->item_at(i)->name();
   }
   return content;
 }
@@ -163,7 +163,7 @@ class ExtensionAppModelBuilderTest : public ExtensionServiceTestBase {
 
 TEST_F(ExtensionAppModelBuilderTest, Build) {
   // The apps list would have 3 extension apps in the profile.
-  EXPECT_EQ(kDefaultAppCount, model_->item_list()->item_count());
+  EXPECT_EQ(kDefaultAppCount, model_->top_level_item_list()->item_count());
   EXPECT_EQ(std::string(kDefaultApps), GetModelContent(model_.get()));
 }
 
@@ -359,6 +359,6 @@ TEST_F(ExtensionAppModelBuilderTest, BookmarkApp) {
   EXPECT_TRUE(err.empty());
 
   service_->AddExtension(bookmark_app.get());
-  EXPECT_EQ(kDefaultAppCount + 1, model_->item_list()->item_count());
+  EXPECT_EQ(kDefaultAppCount + 1, model_->top_level_item_list()->item_count());
   EXPECT_NE(std::string::npos, GetModelContent(model_.get()).find(kAppName));
 }
diff --git a/chrome/browser/ui/app_list/fast_show_pickler.cc b/chrome/browser/ui/app_list/fast_show_pickler.cc
index 500ce01ff31e62..132f82ed027ce2 100644
--- a/chrome/browser/ui/app_list/fast_show_pickler.cc
+++ b/chrome/browser/ui/app_list/fast_show_pickler.cc
@@ -201,19 +201,21 @@ scoped_ptr<Pickle> FastShowPickler::PickleAppListModelForFastShow(
   scoped_ptr<Pickle> result(new Pickle);
   if (!result->WriteInt(kVersion))
     return scoped_ptr<Pickle>();
-  if (!result->WriteInt((int) model->item_list()->item_count()))
+  if (!result->WriteInt((int)model->top_level_item_list()->item_count()))
     return scoped_ptr<Pickle>();
-  for (size_t i = 0; i < model->item_list()->item_count(); ++i) {
-    if (!PickleAppListItem(result.get(), model->item_list()->item_at(i)))
+  for (size_t i = 0; i < model->top_level_item_list()->item_count(); ++i) {
+    if (!PickleAppListItem(result.get(),
+                           model->top_level_item_list()->item_at(i))) {
       return scoped_ptr<Pickle>();
+    }
   }
   return result.Pass();
 }
 
 void FastShowPickler::CopyOver(AppListModel* src, AppListModel* dest) {
-  DCHECK_EQ(0u, dest->item_list()->item_count());
-  for (size_t i = 0; i < src->item_list()->item_count(); i++) {
-    AppListItem* src_item = src->item_list()->item_at(i);
+  DCHECK_EQ(0u, dest->top_level_item_list()->item_count());
+  for (size_t i = 0; i < src->top_level_item_list()->item_count(); i++) {
+    AppListItem* src_item = src->top_level_item_list()->item_at(i);
     scoped_ptr<AppListItem> dest_item(new AppListItem(src_item->id()));
     CopyOverItem(src_item, dest_item.get());
     dest->AddItemToFolder(dest_item.Pass(), src_item->folder_id());
diff --git a/chrome/browser/ui/app_list/test/fast_show_pickler_unittest.cc b/chrome/browser/ui/app_list/test/fast_show_pickler_unittest.cc
index de84eee8a834b2..5451ba11fe2f3f 100644
--- a/chrome/browser/ui/app_list/test/fast_show_pickler_unittest.cc
+++ b/chrome/browser/ui/app_list/test/fast_show_pickler_unittest.cc
@@ -18,16 +18,17 @@ using app_list::AppListModel;
 class AppListModelPicklerUnitTest : public testing::Test {
  protected:
   void CheckIsSame(AppListModel* m1, AppListModel* m2) {
-    ASSERT_EQ(m1->item_list()->item_count(), m2->item_list()->item_count());
-    for (size_t i = 0; i < m1->item_list()->item_count(); i++) {
-      ASSERT_EQ(m1->item_list()->item_at(i)->id(),
-                m2->item_list()->item_at(i)->id());
-      ASSERT_EQ(m1->item_list()->item_at(i)->name(),
-                m2->item_list()->item_at(i)->name());
-      ASSERT_EQ(m1->item_list()->item_at(i)->short_name(),
-                m2->item_list()->item_at(i)->short_name());
-      CompareImages(m1->item_list()->item_at(i)->icon(),
-                    m2->item_list()->item_at(i)->icon());
+    ASSERT_EQ(m1->top_level_item_list()->item_count(),
+              m2->top_level_item_list()->item_count());
+    for (size_t i = 0; i < m1->top_level_item_list()->item_count(); i++) {
+      ASSERT_EQ(m1->top_level_item_list()->item_at(i)->id(),
+                m2->top_level_item_list()->item_at(i)->id());
+      ASSERT_EQ(m1->top_level_item_list()->item_at(i)->name(),
+                m2->top_level_item_list()->item_at(i)->name());
+      ASSERT_EQ(m1->top_level_item_list()->item_at(i)->short_name(),
+                m2->top_level_item_list()->item_at(i)->short_name());
+      CompareImages(m1->top_level_item_list()->item_at(i)->icon(),
+                    m2->top_level_item_list()->item_at(i)->icon());
     }
   }
 
diff --git a/ui/app_list/app_list_folder_item.cc b/ui/app_list/app_list_folder_item.cc
index ecdfdd0500518c..fd77e519ee9db5 100644
--- a/ui/app_list/app_list_folder_item.cc
+++ b/ui/app_list/app_list_folder_item.cc
@@ -178,6 +178,11 @@ size_t AppListFolderItem::ChildItemCount() const {
   return item_list_->item_count();
 }
 
+void AppListFolderItem::OnExtensionPreferenceChanged() {
+  for (size_t i = 0; i < item_list_->item_count(); ++i)
+    item_list_->item_at(i)->OnExtensionPreferenceChanged();
+}
+
 bool AppListFolderItem::CompareForTest(const AppListItem* other) const {
   if (!AppListItem::CompareForTest(other))
     return false;
diff --git a/ui/app_list/app_list_folder_item.h b/ui/app_list/app_list_folder_item.h
index 4fa20cfa17155c..b294e94a3cefb6 100644
--- a/ui/app_list/app_list_folder_item.h
+++ b/ui/app_list/app_list_folder_item.h
@@ -54,6 +54,7 @@ class APP_LIST_EXPORT AppListFolderItem : public AppListItem,
   virtual ui::MenuModel* GetContextMenuModel() OVERRIDE;
   virtual AppListItem* FindChildItem(const std::string& id) OVERRIDE;
   virtual size_t ChildItemCount() const OVERRIDE;
+  virtual void OnExtensionPreferenceChanged() OVERRIDE;
   virtual bool CompareForTest(const AppListItem* other) const OVERRIDE;
 
   // Calculates the top item icons' bounds inside |folder_icon_bounds|.
diff --git a/ui/app_list/app_list_item.cc b/ui/app_list/app_list_item.cc
index 2dc9a866b46ad4..cbb6f864e013c6 100644
--- a/ui/app_list/app_list_item.cc
+++ b/ui/app_list/app_list_item.cc
@@ -84,6 +84,8 @@ size_t AppListItem::ChildItemCount() const {
   return 0;
 }
 
+void AppListItem::OnExtensionPreferenceChanged() {}
+
 bool AppListItem::CompareForTest(const AppListItem* other) const {
   return id_ == other->id_ &&
       folder_id_ == other->folder_id_ &&
diff --git a/ui/app_list/app_list_item.h b/ui/app_list/app_list_item.h
index 5f4d4672fef227..dd92b95a3ebee3 100644
--- a/ui/app_list/app_list_item.h
+++ b/ui/app_list/app_list_item.h
@@ -82,6 +82,10 @@ class APP_LIST_EXPORT AppListItem {
   // Returns the number of child items if it has any (e.g. is a folder) or 0.
   virtual size_t ChildItemCount() const;
 
+  // Called when the extension preference changed. Used by ExtensionAppItem
+  // to update icon overlays.
+  virtual void OnExtensionPreferenceChanged();
+
   // Utility functions for sync integration tests.
   virtual bool CompareForTest(const AppListItem* other) const;
   virtual std::string ToDebugString() const;
diff --git a/ui/app_list/app_list_item_list.cc b/ui/app_list/app_list_item_list.cc
index 3ccff5e6b31ac1..55c6754f707c5c 100644
--- a/ui/app_list/app_list_item_list.cc
+++ b/ui/app_list/app_list_item_list.cc
@@ -49,33 +49,39 @@ void AppListItemList::MoveItem(size_t from_index, size_t to_index) {
     return;
 
   AppListItem* target_item = app_list_items_[from_index];
+  DVLOG(2) << "MoveItem: " << from_index << " -> " << to_index << " ["
+           << target_item->position().ToDebugString() << "]";
+
+  // Remove the target item
   app_list_items_.weak_erase(app_list_items_.begin() + from_index);
-  app_list_items_.insert(app_list_items_.begin() + to_index, target_item);
 
-  // Update position
+  // Update the position
   AppListItem* prev = to_index > 0 ? app_list_items_[to_index - 1] : NULL;
-  AppListItem* next = to_index < app_list_items_.size() - 1 ?
-      app_list_items_[to_index + 1] : NULL;
+  AppListItem* next =
+      to_index < item_count() ? app_list_items_[to_index] : NULL;
   CHECK_NE(prev, next);
-
-  // It is possible that items were added with the same ordinal. Rather than
-  // resolving a potentially complicated chain of conflicts, just set the
-  // ordinal before |next| (which will place it before both items).
-  if (prev && next && prev->position().Equals(next->position()))
-    prev = NULL;
-
   syncer::StringOrdinal new_position;
-  if (!prev)
+  if (!prev) {
     new_position = next->position().CreateBefore();
-  else if (!next)
+  } else if (!next) {
     new_position = prev->position().CreateAfter();
-  else
+  } else {
+    // It is possible that items were added with the same ordinal. To
+    // successfully move the item we need to fix this. We do not try to fix this
+    // when an item is added in order to avoid possible edge cases with sync.
+    if (prev->position().Equals(next->position()))
+      FixItemPosition(to_index);
     new_position = prev->position().CreateBetween(next->position());
-  VLOG(2) << "Move: " << target_item->position().ToDebugString()
-          << " Prev: " << (prev ? prev->position().ToDebugString() : "(none)")
-          << " Next: " << (next ? next->position().ToDebugString() : "(none)")
-          << " -> " << new_position.ToDebugString();
+  }
   target_item->set_position(new_position);
+
+  DVLOG(2) << "Move: "
+           << " Prev: " << (prev ? prev->position().ToDebugString() : "(none)")
+           << " Next: " << (next ? next->position().ToDebugString() : "(none)")
+           << " -> " << new_position.ToDebugString();
+
+  // Insert the item and notify observers.
+  app_list_items_.insert(app_list_items_.begin() + to_index, target_item);
   FOR_EACH_OBSERVER(AppListItemListObserver,
                     observers_,
                     OnListItemMoved(from_index, to_index, target_item));
@@ -95,16 +101,16 @@ void AppListItemList::SetItemPosition(
   // the position.
   size_t to_index = GetItemSortOrderIndex(new_position, item->id());
   if (to_index == from_index) {
-    VLOG(2) << "SetItemPosition: No change: " << item->id().substr(0, 8);
+    DVLOG(2) << "SetItemPosition: No change: " << item->id().substr(0, 8);
     item->set_position(new_position);
     return;
   }
   // Remove the item and get the updated to index.
   app_list_items_.weak_erase(app_list_items_.begin() + from_index);
   to_index = GetItemSortOrderIndex(new_position, item->id());
-  VLOG(2) << "SetItemPosition: " << item->id().substr(0, 8)
-          << " -> " << new_position.ToDebugString()
-          << " From: " << from_index << " To: " << to_index;
+  DVLOG(2) << "SetItemPosition: " << item->id().substr(0, 8) << " -> "
+           << new_position.ToDebugString() << " From: " << from_index
+           << " To: " << to_index;
   item->set_position(new_position);
   app_list_items_.insert(app_list_items_.begin() + to_index, item);
   FOR_EACH_OBSERVER(AppListItemListObserver,
@@ -206,4 +212,31 @@ size_t AppListItemList::GetItemSortOrderIndex(
   return app_list_items_.size();
 }
 
+void AppListItemList::FixItemPosition(size_t index) {
+  DVLOG(1) << "FixItemPosition: " << index;
+  size_t nitems = item_count();
+  DCHECK_LT(index, nitems);
+  DCHECK_GT(index, 0u);
+  // Update the position of |index| and any necessary subsequent items.
+  // First, find the next item that has a different position.
+  AppListItem* prev = app_list_items_[index - 1];
+  size_t last_index = index + 1;
+  for (; last_index < nitems; ++last_index) {
+    if (!app_list_items_[last_index]->position().Equals(prev->position()))
+      break;
+  }
+  AppListItem* last = last_index < nitems ? app_list_items_[last_index] : NULL;
+  for (size_t i = index; i < last_index; ++i) {
+    AppListItem* cur = app_list_items_[i];
+    if (last)
+      cur->set_position(prev->position().CreateBetween(last->position()));
+    else
+      cur->set_position(prev->position().CreateAfter());
+    prev = cur;
+  }
+  FOR_EACH_OBSERVER(AppListItemListObserver,
+                    observers_,
+                    OnListItemMoved(index, index, app_list_items_[index]));
+}
+
 }  // namespace app_list
diff --git a/ui/app_list/app_list_item_list.h b/ui/app_list/app_list_item_list.h
index 95aa342c0c934d..7490c44d5caabf 100644
--- a/ui/app_list/app_list_item_list.h
+++ b/ui/app_list/app_list_item_list.h
@@ -30,6 +30,8 @@ class APP_LIST_EXPORT AppListItemList {
   void RemoveObserver(AppListItemListObserver* observer);
 
   // Finds item matching |id|. NOTE: Requires a linear search.
+  // Generally this should not be used directly, AppListModel::FindItem
+  // should be used instead.
   AppListItem* FindItem(const std::string& id);
 
   // Finds the |index| of the the item matching |id| in |app_list_items_|.
@@ -95,6 +97,10 @@ class APP_LIST_EXPORT AppListItemList {
   size_t GetItemSortOrderIndex(const syncer::StringOrdinal& position,
                                const std::string& id);
 
+  // Fixes the position of the item at |index| when the position matches the
+  // previous item's position. |index| must be > 0.
+  void FixItemPosition(size_t index);
+
   ScopedVector<AppListItem> app_list_items_;
   ObserverList<AppListItemListObserver> observers_;
 
diff --git a/ui/app_list/app_list_item_list_observer.h b/ui/app_list/app_list_item_list_observer.h
index fe8aa24a474b18..640be28a6fff51 100644
--- a/ui/app_list/app_list_item_list_observer.h
+++ b/ui/app_list/app_list_item_list_observer.h
@@ -22,6 +22,7 @@ class APP_LIST_EXPORT AppListItemListObserver {
   virtual void OnListItemRemoved(size_t index, AppListItem* item) {}
 
   // Triggered after |item| has been moved from |from_index| to |to_index|.
+  // Note: |from_index| may equal |to_index| if only the ordinal has changed.
   virtual void OnListItemMoved(size_t from_index,
                                size_t to_index,
                                AppListItem* item) {}
diff --git a/ui/app_list/app_list_item_list_unittest.cc b/ui/app_list/app_list_item_list_unittest.cc
index 8a4b4c93427c6a..93e51518d68f2d 100644
--- a/ui/app_list/app_list_item_list_unittest.cc
+++ b/ui/app_list/app_list_item_list_unittest.cc
@@ -17,10 +17,7 @@ namespace {
 
 class TestObserver : public AppListItemListObserver {
  public:
-  TestObserver()
-      : items_added_(0),
-        items_removed_(0) {
-  }
+  TestObserver() : items_added_(0), items_removed_(0), items_moved_(0) {}
 
   virtual ~TestObserver() {
   }
@@ -34,12 +31,26 @@ class TestObserver : public AppListItemListObserver {
     ++items_removed_;
   }
 
+  virtual void OnListItemMoved(size_t from_index,
+                               size_t to_index,
+                               AppListItem* item) OVERRIDE {
+    ++items_moved_;
+  }
+
   size_t items_added() const { return items_added_; }
   size_t items_removed() const { return items_removed_; }
+  size_t items_moved() const { return items_moved_; }
+
+  void ResetCounts() {
+    items_added_ = 0;
+    items_removed_ = 0;
+    items_moved_ = 0;
+  }
 
  private:
   size_t items_added_;
   size_t items_removed_;
+  size_t items_moved_;
 
   DISALLOW_COPY_AND_ASSIGN(TestObserver);
 };
@@ -65,6 +76,14 @@ class AppListItemListTest : public testing::Test {
   }
 
  protected:
+  AppListItem* FindItem(const std::string& id) {
+    return item_list_.FindItem(id);
+  }
+
+  bool FindItemIndex(const std::string& id, size_t* index) {
+    return item_list_.FindItemIndex(id, index);
+  }
+
   scoped_ptr<AppListItem> CreateItem(const std::string& name) {
     scoped_ptr<AppListItem> item(new AppListItem(name));
     size_t nitems = item_list_.item_count();
@@ -141,15 +160,15 @@ TEST_F(AppListItemListTest, FindItemIndex) {
   EXPECT_TRUE(VerifyItemListOrdinals());
 
   size_t index;
-  EXPECT_TRUE(item_list_.FindItemIndex(item_0->id(), &index));
+  EXPECT_TRUE(FindItemIndex(item_0->id(), &index));
   EXPECT_EQ(index, 0u);
-  EXPECT_TRUE(item_list_.FindItemIndex(item_1->id(), &index));
+  EXPECT_TRUE(FindItemIndex(item_1->id(), &index));
   EXPECT_EQ(index, 1u);
-  EXPECT_TRUE(item_list_.FindItemIndex(item_2->id(), &index));
+  EXPECT_TRUE(FindItemIndex(item_2->id(), &index));
   EXPECT_EQ(index, 2u);
 
   scoped_ptr<AppListItem> item_3(CreateItem(GetItemId(3)));
-  EXPECT_FALSE(item_list_.FindItemIndex(item_3->id(), &index));
+  EXPECT_FALSE(FindItemIndex(item_3->id(), &index));
 }
 
 TEST_F(AppListItemListTest, RemoveItemAt) {
@@ -159,13 +178,13 @@ TEST_F(AppListItemListTest, RemoveItemAt) {
   EXPECT_EQ(item_list_.item_count(), 3u);
   EXPECT_EQ(observer_.items_added(), 3u);
   size_t index;
-  EXPECT_TRUE(item_list_.FindItemIndex(item_1->id(), &index));
+  EXPECT_TRUE(FindItemIndex(item_1->id(), &index));
   EXPECT_EQ(index, 1u);
   EXPECT_TRUE(VerifyItemListOrdinals());
 
   scoped_ptr<AppListItem> item_removed = RemoveItemAt(1);
   EXPECT_EQ(item_removed, item_1);
-  EXPECT_FALSE(item_list_.FindItem(item_1->id()));
+  EXPECT_FALSE(FindItem(item_1->id()));
   EXPECT_EQ(item_list_.item_count(), 2u);
   EXPECT_EQ(observer_.items_removed(), 1u);
   EXPECT_EQ(item_list_.item_at(0), item_0);
@@ -185,12 +204,12 @@ TEST_F(AppListItemListTest, RemoveItem) {
   EXPECT_TRUE(VerifyItemListOrdinals());
 
   size_t index;
-  EXPECT_TRUE(item_list_.FindItemIndex(item_1->id(), &index));
+  EXPECT_TRUE(FindItemIndex(item_1->id(), &index));
   EXPECT_EQ(index, 1u);
 
   scoped_ptr<AppListItem> item_removed = RemoveItem(item_1->id());
   EXPECT_EQ(item_removed, item_1);
-  EXPECT_FALSE(item_list_.FindItem(item_1->id()));
+  EXPECT_FALSE(FindItem(item_1->id()));
   EXPECT_EQ(item_list_.item_count(), 2u);
   EXPECT_EQ(observer_.items_removed(), 1u);
   EXPECT_TRUE(VerifyItemListOrdinals());
@@ -204,27 +223,85 @@ TEST_F(AppListItemListTest, MoveItem) {
   CreateAndAddItem(GetItemId(1));
   CreateAndAddItem(GetItemId(2));
   CreateAndAddItem(GetItemId(3));
+
+  EXPECT_TRUE(VerifyItemOrder4(0, 1, 2, 3));
+
+  item_list_.MoveItem(0, 0);
+  EXPECT_EQ(0u, observer_.items_moved());
   EXPECT_TRUE(VerifyItemOrder4(0, 1, 2, 3));
 
   item_list_.MoveItem(0, 1);
+  EXPECT_EQ(1u, observer_.items_moved());
   EXPECT_TRUE(VerifyItemListOrdinals());
   EXPECT_TRUE(VerifyItemOrder4(1, 0, 2, 3));
 
   item_list_.MoveItem(1, 2);
+  EXPECT_EQ(2u, observer_.items_moved());
   EXPECT_TRUE(VerifyItemListOrdinals());
   EXPECT_TRUE(VerifyItemOrder4(1, 2, 0, 3));
 
-  item_list_.MoveItem(2, 3);
+  item_list_.MoveItem(2, 1);
+  EXPECT_EQ(3u, observer_.items_moved());
   EXPECT_TRUE(VerifyItemListOrdinals());
-  EXPECT_TRUE(VerifyItemOrder4(1, 2, 3, 0));
+  EXPECT_TRUE(VerifyItemOrder4(1, 0, 2, 3));
 
   item_list_.MoveItem(3, 0);
+  EXPECT_EQ(4u, observer_.items_moved());
   EXPECT_TRUE(VerifyItemListOrdinals());
-  EXPECT_TRUE(VerifyItemOrder4(0, 1, 2, 3));
+  EXPECT_TRUE(VerifyItemOrder4(3, 1, 0, 2));
 
   item_list_.MoveItem(0, 3);
+  EXPECT_EQ(5u, observer_.items_moved());
   EXPECT_TRUE(VerifyItemListOrdinals());
-  EXPECT_TRUE(VerifyItemOrder4(1, 2, 3, 0));
+  EXPECT_TRUE(VerifyItemOrder4(1, 0, 2, 3));
+}
+
+TEST_F(AppListItemListTest, SamePosition) {
+  CreateAndAddItem(GetItemId(0));
+  CreateAndAddItem(GetItemId(1));
+  CreateAndAddItem(GetItemId(2));
+  CreateAndAddItem(GetItemId(3));
+  item_list_.SetItemPosition(item_list_.item_at(2),
+                             item_list_.item_at(1)->position());
+  EXPECT_TRUE(VerifyItemOrder4(0, 1, 2, 3));
+  EXPECT_TRUE(item_list_.item_at(1)->position().Equals(
+      item_list_.item_at(2)->position()));
+  // Moving an item to position 1 should fix the position.
+  observer_.ResetCounts();
+  item_list_.MoveItem(0, 1);
+  EXPECT_TRUE(VerifyItemOrder4(1, 0, 2, 3));
+  EXPECT_TRUE(item_list_.item_at(0)->position().LessThan(
+      item_list_.item_at(1)->position()));
+  EXPECT_TRUE(item_list_.item_at(1)->position().LessThan(
+      item_list_.item_at(2)->position()));
+  EXPECT_TRUE(item_list_.item_at(2)->position().LessThan(
+      item_list_.item_at(3)->position()));
+  // One extra move notification for fixed position.
+  EXPECT_EQ(2u, observer_.items_moved());
+
+  // Restore the original order.
+  item_list_.MoveItem(1, 0);
+  EXPECT_TRUE(VerifyItemOrder4(0, 1, 2, 3));
+
+  // Set all four items to the same position.
+  item_list_.SetItemPosition(item_list_.item_at(1),
+                             item_list_.item_at(0)->position());
+  item_list_.SetItemPosition(item_list_.item_at(2),
+                             item_list_.item_at(0)->position());
+  item_list_.SetItemPosition(item_list_.item_at(3),
+                             item_list_.item_at(0)->position());
+  // Move should fix the position of the items.
+  observer_.ResetCounts();
+  item_list_.MoveItem(0, 1);
+  EXPECT_TRUE(VerifyItemOrder4(1, 0, 2, 3));
+  EXPECT_TRUE(item_list_.item_at(0)->position().LessThan(
+      item_list_.item_at(1)->position()));
+  EXPECT_TRUE(item_list_.item_at(1)->position().LessThan(
+      item_list_.item_at(2)->position()));
+  EXPECT_TRUE(item_list_.item_at(2)->position().LessThan(
+      item_list_.item_at(3)->position()));
+  // One extra move notification for fixed position.
+  EXPECT_EQ(2u, observer_.items_moved());
 }
 
 TEST_F(AppListItemListTest, CreatePositionBefore) {
diff --git a/ui/app_list/app_list_model.cc b/ui/app_list/app_list_model.cc
index 5cdd6803316a6a..e79737e18bbb2a 100644
--- a/ui/app_list/app_list_model.cc
+++ b/ui/app_list/app_list_model.cc
@@ -15,16 +15,14 @@
 namespace app_list {
 
 AppListModel::AppListModel()
-    : item_list_(new AppListItemList),
+    : top_level_item_list_(new AppListItemList),
       search_box_(new SearchBoxModel),
       results_(new SearchResults),
       status_(STATUS_NORMAL) {
-  item_list_->AddObserver(this);
+  top_level_item_list_->AddObserver(this);
 }
 
-AppListModel::~AppListModel() {
-  item_list_->RemoveObserver(this);
-}
+AppListModel::~AppListModel() { top_level_item_list_->RemoveObserver(this); }
 
 void AppListModel::AddObserver(AppListModelObserver* observer) {
   observers_.AddObserver(observer);
@@ -45,11 +43,12 @@ void AppListModel::SetStatus(Status status) {
 }
 
 AppListItem* AppListModel::FindItem(const std::string& id) {
-  AppListItem* item = item_list_->FindItem(id);
+  AppListItem* item = top_level_item_list_->FindItem(id);
   if (item)
     return item;
-  for (size_t i = 0; i < item_list_->item_count(); ++i) {
-    AppListItem* child_item = item_list_->item_at(i)->FindChildItem(id);
+  for (size_t i = 0; i < top_level_item_list_->item_count(); ++i) {
+    AppListItem* child_item =
+        top_level_item_list_->item_at(i)->FindChildItem(id);
     if (child_item)
       return child_item;
   }
@@ -57,7 +56,7 @@ AppListItem* AppListModel::FindItem(const std::string& id) {
 }
 
 AppListFolderItem* AppListModel::FindFolderItem(const std::string& id) {
-  AppListItem* item = item_list_->FindItem(id);
+  AppListItem* item = top_level_item_list_->FindItem(id);
   if (item && item->GetItemType() == AppListFolderItem::kItemType)
     return static_cast<AppListFolderItem*>(item);
   DCHECK(!item);
@@ -66,7 +65,7 @@ AppListFolderItem* AppListModel::FindFolderItem(const std::string& id) {
 
 AppListItem* AppListModel::AddItem(scoped_ptr<AppListItem> item) {
   DCHECK(!item->IsInFolder());
-  DCHECK(!item_list()->FindItem(item->id()));
+  DCHECK(!top_level_item_list()->FindItem(item->id()));
   return AddItemToItemListAndNotify(item.Pass());
 }
 
@@ -104,14 +103,15 @@ const std::string& AppListModel::MergeItems(const std::string& target_item_id,
     return target_folder->id();
   }
 
-  // Otherwise, remove the target item from |item_list_|, it will become owned
-  // by the new folder.
+  // Otherwise, remove the target item from |top_level_item_list_|, it will
+  // become owned by the new folder.
   scoped_ptr<AppListItem> target_item_ptr =
-      item_list_->RemoveItem(target_item_id);
+      top_level_item_list_->RemoveItem(target_item_id);
 
   // Create a new folder in the same location as the target item.
-  scoped_ptr<AppListItem> new_folder_ptr(
-      new AppListFolderItem(AppListFolderItem::GenerateId()));
+  std::string new_folder_id = AppListFolderItem::GenerateId();
+  DVLOG(2) << "Creating folder for merge: " << new_folder_id;
+  scoped_ptr<AppListItem> new_folder_ptr(new AppListFolderItem(new_folder_id));
   new_folder_ptr->set_position(target_item->position());
   AppListFolderItem* new_folder = static_cast<AppListFolderItem*>(
       AddItemToItemListAndNotify(new_folder_ptr.Pass()));
@@ -158,7 +158,8 @@ void AppListModel::MoveItemToFolderAt(AppListItem* item,
         dest_folder->item_list()->CreatePositionBefore(position));
     AddItemToFolderItemAndNotify(dest_folder, item_ptr.Pass());
   } else {
-    item_ptr->set_position(item_list_->CreatePositionBefore(position));
+    item_ptr->set_position(
+        top_level_item_list_->CreatePositionBefore(position));
     AddItemToItemListAndNotifyUpdate(item_ptr.Pass());
   }
 }
@@ -166,7 +167,7 @@ void AppListModel::MoveItemToFolderAt(AppListItem* item,
 void AppListModel::SetItemPosition(AppListItem* item,
                                    const syncer::StringOrdinal& new_position) {
   if (!item->IsInFolder()) {
-    item_list_->SetItemPosition(item, new_position);
+    top_level_item_list_->SetItemPosition(item, new_position);
     // Note: this will trigger OnListItemMoved which will signal observers.
     // (This is done this way because some View code still moves items within
     // the item list directly).
@@ -209,7 +210,7 @@ void AppListModel::DeleteItem(const std::string& id) {
     FOR_EACH_OBSERVER(AppListModelObserver,
                       observers_,
                       OnAppListItemWillBeDeleted(item));
-    item_list_->DeleteItem(id);
+    top_level_item_list_->DeleteItem(id);
     return;
   }
   AppListFolderItem* folder = FindFolderItem(item->folder_id());
@@ -222,6 +223,11 @@ void AppListModel::DeleteItem(const std::string& id) {
   child_item.reset();  // Deletes item.
 }
 
+void AppListModel::NotifyExtensionPreferenceChanged() {
+  for (size_t i = 0; i < top_level_item_list_->item_count(); ++i)
+    top_level_item_list_->item_at(i)->OnExtensionPreferenceChanged();
+}
+
 // Private methods
 
 void AppListModel::OnListItemMoved(size_t from_index,
@@ -241,9 +247,10 @@ AppListFolderItem* AppListModel::FindOrCreateFolderItem(
   if (dest_folder)
     return dest_folder;
 
+  DVLOG(2) << "Creating new folder: " << folder_id;
   scoped_ptr<AppListFolderItem> new_folder(new AppListFolderItem(folder_id));
   new_folder->set_position(
-      item_list_->CreatePositionBefore(syncer::StringOrdinal()));
+      top_level_item_list_->CreatePositionBefore(syncer::StringOrdinal()));
   AppListItem* new_folder_item =
       AddItemToItemListAndNotify(new_folder.PassAs<AppListItem>());
   return static_cast<AppListFolderItem*>(new_folder_item);
@@ -252,7 +259,7 @@ AppListFolderItem* AppListModel::FindOrCreateFolderItem(
 AppListItem* AppListModel::AddItemToItemListAndNotify(
     scoped_ptr<AppListItem> item_ptr) {
   DCHECK(!item_ptr->IsInFolder());
-  AppListItem* item = item_list_->AddItem(item_ptr.Pass());
+  AppListItem* item = top_level_item_list_->AddItem(item_ptr.Pass());
   FOR_EACH_OBSERVER(AppListModelObserver,
                     observers_,
                     OnAppListItemAdded(item));
@@ -262,7 +269,7 @@ AppListItem* AppListModel::AddItemToItemListAndNotify(
 AppListItem* AppListModel::AddItemToItemListAndNotifyUpdate(
     scoped_ptr<AppListItem> item_ptr) {
   DCHECK(!item_ptr->IsInFolder());
-  AppListItem* item = item_list_->AddItem(item_ptr.Pass());
+  AppListItem* item = top_level_item_list_->AddItem(item_ptr.Pass());
   FOR_EACH_OBSERVER(AppListModelObserver,
                     observers_,
                     OnAppListItemUpdated(item));
@@ -282,10 +289,9 @@ AppListItem* AppListModel::AddItemToFolderItemAndNotify(
 
 scoped_ptr<AppListItem> AppListModel::RemoveItem(AppListItem* item) {
   if (!item->IsInFolder())
-    return item_list_->RemoveItem(item->id());
+    return top_level_item_list_->RemoveItem(item->id());
 
   AppListFolderItem* folder = FindFolderItem(item->folder_id());
-  DCHECK(folder);
   return RemoveItemFromFolder(folder, item);
 }
 
diff --git a/ui/app_list/app_list_model.h b/ui/app_list/app_list_model.h
index 76d4e357eed788..6d71e0b6a600a9 100644
--- a/ui/app_list/app_list_model.h
+++ b/ui/app_list/app_list_model.h
@@ -26,7 +26,7 @@ class SearchResult;
 // SearchBoxModel and SearchResults. The AppListItemList sub model owns a list
 // of AppListItems and is displayed in the grid view. SearchBoxModel is
 // the model for SearchBoxView. SearchResults owns a list of SearchResult.
-// NOTE: Currently this class observes |item_list_|. The View code may
+// NOTE: Currently this class observes |top_level_item_list_|. The View code may
 // move entries in the item list directly (but can not add or remove them) and
 // the model needs to notify its observers when this occurs.
 class APP_LIST_EXPORT AppListModel : public AppListItemListObserver {
@@ -85,8 +85,8 @@ class APP_LIST_EXPORT AppListModel : public AppListItemListObserver {
                           const std::string& folder_id,
                           syncer::StringOrdinal position);
 
-  // Sets the position of |item| either in |item_list_| or the folder specified
-  // by |item|->folder_id().
+  // Sets the position of |item| either in |top_level_item_list_| or the folder
+  // specified by |item|->folder_id().
   void SetItemPosition(AppListItem* item,
                        const syncer::StringOrdinal& new_position);
 
@@ -98,10 +98,15 @@ class APP_LIST_EXPORT AppListModel : public AppListItemListObserver {
                                const std::string& name,
                                const std::string& short_name);
 
-  // Deletes the item matching |id| from |item_list_| or from its folder.
+  // Deletes the item matching |id| from |top_level_item_list_| or from the
+  // appropriate folder.
   void DeleteItem(const std::string& id);
 
-  AppListItemList* item_list() { return item_list_.get(); }
+  // Call OnExtensionPreferenceChanged() for all items in the model.
+  void NotifyExtensionPreferenceChanged();
+
+  AppListItemList* top_level_item_list() { return top_level_item_list_.get(); }
+
   SearchBoxModel* search_box() { return search_box_.get(); }
   SearchResults* results() { return results_.get(); }
   Status status() const { return status_; }
@@ -115,12 +120,12 @@ class APP_LIST_EXPORT AppListModel : public AppListItemListObserver {
   // Returns an existing folder matching |folder_id| or creates a new folder.
   AppListFolderItem* FindOrCreateFolderItem(const std::string& folder_id);
 
-  // Adds |item_ptr| to |item_list_| and notifies observers.
+  // Adds |item_ptr| to |top_level_item_list_| and notifies observers.
   AppListItem* AddItemToItemListAndNotify(
       scoped_ptr<AppListItem> item_ptr);
 
-  // Adds |item_ptr| to |item_list_| and notifies observers that an Update
-  // occured (e.g. item moved from a folder).
+  // Adds |item_ptr| to |top_level_item_list_| and notifies observers that an
+  // Update occured (e.g. item moved from a folder).
   AppListItem* AddItemToItemListAndNotifyUpdate(
       scoped_ptr<AppListItem> item_ptr);
 
@@ -128,16 +133,18 @@ class APP_LIST_EXPORT AppListModel : public AppListItemListObserver {
   AppListItem* AddItemToFolderItemAndNotify(AppListFolderItem* folder,
                                             scoped_ptr<AppListItem> item_ptr);
 
-  // Removes |item| from |item_list_| or calls RemoveItemFromFolder if
+  // Removes |item| from |top_level_item_list_| or calls RemoveItemFromFolder if
   // |item|->folder_id is set.
   scoped_ptr<AppListItem> RemoveItem(AppListItem* item);
 
   // Removes |item| from |folder|. If |folder| becomes empty, deletes |folder|
-  // from |item_list_|. Does NOT trigger observers, calling function must do so.
+  // from |top_level_item_list_|. Does NOT trigger observers, calling function
+  // must do so.
   scoped_ptr<AppListItem> RemoveItemFromFolder(AppListFolderItem* folder,
                                                AppListItem* item);
 
-  scoped_ptr<AppListItemList> item_list_;
+  scoped_ptr<AppListItemList> top_level_item_list_;
+
   scoped_ptr<SearchBoxModel> search_box_;
   scoped_ptr<SearchResults> results_;
 
diff --git a/ui/app_list/app_list_model_unittest.cc b/ui/app_list/app_list_model_unittest.cc
index 629f5eb14603ce..4d16f1666d6b91 100644
--- a/ui/app_list/app_list_model_unittest.cc
+++ b/ui/app_list/app_list_model_unittest.cc
@@ -102,7 +102,7 @@ class AppListModelTest : public testing::Test {
   }
 
   std::string GetModelContents() {
-    return GetItemListContents(model_.item_list());
+    return GetItemListContents(model_.top_level_item_list());
   }
 
   test::AppListTestModel model_;
@@ -133,10 +133,10 @@ TEST_F(AppListModelTest, AppsObserver) {
 TEST_F(AppListModelTest, ModelGetItem) {
   const size_t num_apps = 2;
   model_.PopulateApps(num_apps);
-  AppListItem* item0 = model_.item_list()->item_at(0);
+  AppListItem* item0 = model_.top_level_item_list()->item_at(0);
   ASSERT_TRUE(item0);
   EXPECT_EQ(model_.GetItemName(0), item0->id());
-  AppListItem* item1 = model_.item_list()->item_at(1);
+  AppListItem* item1 = model_.top_level_item_list()->item_at(1);
   ASSERT_TRUE(item1);
   EXPECT_EQ(model_.GetItemName(1), item1->id());
 }
@@ -159,19 +159,20 @@ TEST_F(AppListModelTest, SetItemPosition) {
   model_.PopulateApps(num_apps);
   // Adding another item will add it to the end.
   model_.CreateAndAddItem("Added Item 1");
-  ASSERT_EQ(num_apps + 1, model_.item_list()->item_count());
-  EXPECT_EQ("Added Item 1", model_.item_list()->item_at(num_apps)->id());
+  ASSERT_EQ(num_apps + 1, model_.top_level_item_list()->item_count());
+  EXPECT_EQ("Added Item 1",
+            model_.top_level_item_list()->item_at(num_apps)->id());
   // Add an item between items 0 and 1.
-  AppListItem* item0 = model_.item_list()->item_at(0);
+  AppListItem* item0 = model_.top_level_item_list()->item_at(0);
   ASSERT_TRUE(item0);
-  AppListItem* item1 = model_.item_list()->item_at(1);
+  AppListItem* item1 = model_.top_level_item_list()->item_at(1);
   ASSERT_TRUE(item1);
   AppListItem* item2 = model_.CreateItem("Added Item 2");
   model_.AddItem(item2);
   EXPECT_EQ("Item 0,Item 1,Added Item 1,Added Item 2", GetModelContents());
   model_.SetItemPosition(
       item2, item0->position().CreateBetween(item1->position()));
-  EXPECT_EQ(num_apps + 2, model_.item_list()->item_count());
+  EXPECT_EQ(num_apps + 2, model_.top_level_item_list()->item_count());
   EXPECT_EQ(num_apps + 2, observer_.items_added());
   EXPECT_EQ("Item 0,Added Item 2,Item 1,Added Item 1", GetModelContents());
 }
@@ -181,10 +182,10 @@ TEST_F(AppListModelTest, ModelMoveItem) {
   model_.PopulateApps(num_apps);
   // Adding another item will add it to the end.
   model_.CreateAndAddItem("Inserted Item");
-  ASSERT_EQ(num_apps + 1, model_.item_list()->item_count());
+  ASSERT_EQ(num_apps + 1, model_.top_level_item_list()->item_count());
   // Move it to the position 1.
   observer_.ResetCounts();
-  model_.item_list()->MoveItem(num_apps, 1);
+  model_.top_level_item_list()->MoveItem(num_apps, 1);
   EXPECT_EQ(1u, observer_.items_updated());
   EXPECT_EQ("Item 0,Inserted Item,Item 1,Item 2", GetModelContents());
 }
@@ -194,17 +195,17 @@ TEST_F(AppListModelTest, ModelRemoveItem) {
   model_.PopulateApps(num_apps);
   // Remove an item in the middle.
   model_.DeleteItem(model_.GetItemName(1));
-  EXPECT_EQ(num_apps - 1, model_.item_list()->item_count());
+  EXPECT_EQ(num_apps - 1, model_.top_level_item_list()->item_count());
   EXPECT_EQ(1u, observer_.items_removed());
   EXPECT_EQ("Item 0,Item 2,Item 3", GetModelContents());
   // Remove the first item in the list.
   model_.DeleteItem(model_.GetItemName(0));
-  EXPECT_EQ(num_apps - 2, model_.item_list()->item_count());
+  EXPECT_EQ(num_apps - 2, model_.top_level_item_list()->item_count());
   EXPECT_EQ(2u, observer_.items_removed());
   EXPECT_EQ("Item 2,Item 3", GetModelContents());
   // Remove the last item in the list.
   model_.DeleteItem(model_.GetItemName(num_apps - 1));
-  EXPECT_EQ(num_apps - 3, model_.item_list()->item_count());
+  EXPECT_EQ(num_apps - 3, model_.top_level_item_list()->item_count());
   EXPECT_EQ(3u, observer_.items_removed());
   EXPECT_EQ("Item 2", GetModelContents());
 }
@@ -214,15 +215,17 @@ TEST_F(AppListModelTest, AppOrder) {
   model_.PopulateApps(num_apps);
   // Ensure order is preserved.
   for (size_t i = 1; i < num_apps; ++i) {
-    EXPECT_TRUE(model_.item_list()->item_at(i)->position().GreaterThan(
-        model_.item_list()->item_at(i - 1)->position()));
+    EXPECT_TRUE(
+        model_.top_level_item_list()->item_at(i)->position().GreaterThan(
+            model_.top_level_item_list()->item_at(i - 1)->position()));
   }
   // Move an app
-  model_.item_list()->MoveItem(num_apps - 1, 1);
+  model_.top_level_item_list()->MoveItem(num_apps - 1, 1);
   // Ensure order is preserved.
   for (size_t i = 1; i < num_apps; ++i) {
-    EXPECT_TRUE(model_.item_list()->item_at(i)->position().GreaterThan(
-        model_.item_list()->item_at(i - 1)->position()));
+    EXPECT_TRUE(
+        model_.top_level_item_list()->item_at(i)->position().GreaterThan(
+            model_.top_level_item_list()->item_at(i - 1)->position()));
   }
 }
 
@@ -281,21 +284,21 @@ TEST_F(AppListModelFolderTest, FolderItem) {
 
 TEST_F(AppListModelFolderTest, MergeItems) {
   model_.PopulateApps(3);
-  ASSERT_EQ(3u, model_.item_list()->item_count());
-  AppListItem* item0 = model_.item_list()->item_at(0);
-  AppListItem* item1 = model_.item_list()->item_at(1);
-  AppListItem* item2 = model_.item_list()->item_at(2);
+  ASSERT_EQ(3u, model_.top_level_item_list()->item_count());
+  AppListItem* item0 = model_.top_level_item_list()->item_at(0);
+  AppListItem* item1 = model_.top_level_item_list()->item_at(1);
+  AppListItem* item2 = model_.top_level_item_list()->item_at(2);
 
   // Merge two items.
   std::string folder1_id = model_.MergeItems(item0->id(), item1->id());
-  ASSERT_EQ(2u, model_.item_list()->item_count());  // Folder + 1 item
+  ASSERT_EQ(2u, model_.top_level_item_list()->item_count());  // Folder + 1 item
   AppListFolderItem* folder1_item = model_.FindFolderItem(folder1_id);
   ASSERT_TRUE(folder1_item);
   EXPECT_EQ("Item 0,Item 1", GetItemListContents(folder1_item->item_list()));
 
   // Merge an item from the new folder into the third item.
   std::string folder2_id = model_.MergeItems(item2->id(), item1->id());
-  ASSERT_EQ(2u, model_.item_list()->item_count());  // 2 folders
+  ASSERT_EQ(2u, model_.top_level_item_list()->item_count());  // 2 folders
   AppListFolderItem* folder2_item = model_.FindFolderItem(folder2_id);
   EXPECT_EQ("Item 0", GetItemListContents(folder1_item->item_list()));
   EXPECT_EQ("Item 2,Item 1", GetItemListContents(folder2_item->item_list()));
@@ -316,7 +319,7 @@ TEST_F(AppListModelFolderTest, AddItemToFolder) {
   model_.AddItem(folder);
   AppListItem* item0 = new AppListItem("Item 0");
   model_.AddItemToFolder(item0, folder->id());
-  ASSERT_EQ(1u, model_.item_list()->item_count());
+  ASSERT_EQ(1u, model_.top_level_item_list()->item_count());
   AppListFolderItem* folder_item = model_.FindFolderItem(folder->id());
   ASSERT_TRUE(folder_item);
   ASSERT_EQ(1u, folder_item->item_list()->item_count());
@@ -331,7 +334,7 @@ TEST_F(AppListModelFolderTest, MoveItemToFolder) {
   AppListItem* item1 = new AppListItem("Item 1");
   model_.AddItem(item0);
   model_.AddItem(item1);
-  ASSERT_EQ(3u, model_.item_list()->item_count());
+  ASSERT_EQ(3u, model_.top_level_item_list()->item_count());
   // Move item0 and item1 to folder.
   std::string folder_id = folder->id();
   model_.MoveItemToFolder(item0, folder_id);
@@ -360,15 +363,16 @@ TEST_F(AppListModelFolderTest, MoveItemToFolderAt) {
       model_.AddItem(new AppListFolderItem("folder1")));
   model_.AddItem(new AppListItem("Item 2"));
   model_.AddItem(new AppListItem("Item 3"));
-  ASSERT_EQ(5u, model_.item_list()->item_count());
+  ASSERT_EQ(5u, model_.top_level_item_list()->item_count());
   EXPECT_EQ("Item 0,Item 1,folder1,Item 2,Item 3", GetModelContents());
   // Move Item 1 to folder1, then Item 2 before Item 1.
-  model_.MoveItemToFolderAt(
-      model_.item_list()->item_at(1), folder1->id(), syncer::StringOrdinal());
+  model_.MoveItemToFolderAt(model_.top_level_item_list()->item_at(1),
+                            folder1->id(),
+                            syncer::StringOrdinal());
   EXPECT_EQ("Item 0,folder1,Item 2,Item 3", GetModelContents());
-  model_.MoveItemToFolderAt(
-      model_.item_list()->item_at(2), folder1->id(),
-      folder1->item_list()->item_at(0)->position());
+  model_.MoveItemToFolderAt(model_.top_level_item_list()->item_at(2),
+                            folder1->id(),
+                            folder1->item_list()->item_at(0)->position());
   EXPECT_EQ("Item 2,Item 1", GetItemListContents(folder1->item_list()));
   EXPECT_EQ("Item 0,folder1,Item 3", GetModelContents());
   // Move Item 2 out of folder to before folder.
@@ -406,14 +410,14 @@ TEST_F(AppListModelFolderTest, MoveItemFromFolderToFolder) {
 
   // Move item1 from folder0 to folder1. folder0 should get deleted.
   model_.MoveItemToFolder(item1, folder1->id());
-  ASSERT_EQ(1u, model_.item_list()->item_count());
+  ASSERT_EQ(1u, model_.top_level_item_list()->item_count());
   ASSERT_EQ(2u, folder1->item_list()->item_count());
   EXPECT_EQ(folder1->id(), item1->folder_id());
   EXPECT_EQ("Item 0,Item 1", GetItemListContents(folder1->item_list()));
 
   // Move item1 to a non-existant folder2 which should get created.
   model_.MoveItemToFolder(item1, "folder2");
-  ASSERT_EQ(2u, model_.item_list()->item_count());
+  ASSERT_EQ(2u, model_.top_level_item_list()->item_count());
   ASSERT_EQ(1u, folder1->item_list()->item_count());
   EXPECT_EQ("folder2", item1->folder_id());
   AppListFolderItem* folder2 = model_.FindFolderItem("folder2");
diff --git a/ui/app_list/cocoa/apps_grid_controller.mm b/ui/app_list/cocoa/apps_grid_controller.mm
index 998b11e93e66d5..38fec6fdc44616 100644
--- a/ui/app_list/cocoa/apps_grid_controller.mm
+++ b/ui/app_list/cocoa/apps_grid_controller.mm
@@ -191,7 +191,7 @@ - (void)setDelegate:(app_list::AppListViewDelegate*)newDelegate {
   if (delegate_) {
     app_list::AppListModel* oldModel = delegate_->GetModel();
     if (oldModel)
-      oldModel->item_list()->RemoveObserver(bridge_.get());
+      oldModel->top_level_item_list()->RemoveObserver(bridge_.get());
   }
 
   // Since the old model may be getting deleted, and the AppKit objects might
@@ -212,9 +212,10 @@ - (void)setDelegate:(app_list::AppListViewDelegate*)newDelegate {
   if (!newModel)
     return;
 
-  newModel->item_list()->AddObserver(bridge_.get());
-  for (size_t i = 0; i < newModel->item_list()->item_count(); ++i) {
-    app_list::AppListItem* itemModel = newModel->item_list()->item_at(i);
+  newModel->top_level_item_list()->AddObserver(bridge_.get());
+  for (size_t i = 0; i < newModel->top_level_item_list()->item_count(); ++i) {
+    app_list::AppListItem* itemModel =
+        newModel->top_level_item_list()->item_at(i);
     [items_ insertObject:[NSValue valueWithPointer:itemModel]
                  atIndex:i];
   }
@@ -526,7 +527,7 @@ - (void)moveItemWithIndex:(size_t)itemIndex
   if (itemIndex == modelIndex)
     return;
 
-  app_list::AppListItemList* itemList = [self model]->item_list();
+  app_list::AppListItemList* itemList = [self model]->top_level_item_list();
   itemList->RemoveObserver(bridge_.get());
   itemList->MoveItem(itemIndex, modelIndex);
   itemList->AddObserver(bridge_.get());
diff --git a/ui/app_list/cocoa/apps_grid_controller_unittest.mm b/ui/app_list/cocoa/apps_grid_controller_unittest.mm
index 4f22f18e4856b2..13634d818b9938 100644
--- a/ui/app_list/cocoa/apps_grid_controller_unittest.mm
+++ b/ui/app_list/cocoa/apps_grid_controller_unittest.mm
@@ -448,7 +448,8 @@ void SetMenuReadyForTesting(bool ready) {
   EXPECT_EQ(std::string("|Item 0,Item 1,Item 2|"), GetViewContent());
 
   // Update the title via the ItemModelObserver.
-  app_list::AppListItem* item_model = model()->item_list()->item_at(2);
+  app_list::AppListItem* item_model =
+      model()->top_level_item_list()->item_at(2);
   model()->SetItemName(item_model, "UpdatedItem");
   EXPECT_NSEQ(@"UpdatedItem", [button title]);
 
@@ -473,7 +474,7 @@ void SetMenuReadyForTesting(bool ready) {
   EXPECT_EQ(2u, [[GetPageAt(0) content] count]);
   EXPECT_EQ(std::string("|Item 0,Item 1|"), GetViewContent());
 
-  app_list::AppListItemList* item_list = model()->item_list();
+  app_list::AppListItemList* item_list = model()->top_level_item_list();
 
   model()->CreateAndAddItem("Item 2");
   ASSERT_EQ(3u, item_list->item_count());
@@ -497,7 +498,7 @@ void SetMenuReadyForTesting(bool ready) {
   EXPECT_EQ(std::string("|Item 0,Item 1,Item 2|"), GetViewContent());
 
   // Test swapping items (e.g. rearranging via sync).
-  model()->item_list()->MoveItem(1, 2);
+  model()->top_level_item_list()->MoveItem(1, 2);
   EXPECT_EQ(std::string("|Item 0,Item 2,Item 1|"), GetViewContent());
 }
 
@@ -534,7 +535,7 @@ void SetMenuReadyForTesting(bool ready) {
 }
 
 TEST_F(AppsGridControllerTest, ModelRemovePage) {
-  app_list::AppListItemList* item_list = model()->item_list();
+  app_list::AppListItemList* item_list = model()->top_level_item_list();
 
   model()->PopulateApps(kItemsPerPage + 1);
   ASSERT_EQ(kItemsPerPage + 1, item_list->item_count());
@@ -555,7 +556,7 @@ void SetMenuReadyForTesting(bool ready) {
   EXPECT_EQ(2u, [apps_grid_controller_ pageCount]);
   EXPECT_EQ(0u, [apps_grid_controller_ visiblePage]);
   app_list::AppListItem* item_model =
-      model()->item_list()->item_at(kItemsPerPage);
+      model()->top_level_item_list()->item_at(kItemsPerPage);
 
   // Highlighting an item should activate the page it is on.
   item_model->SetHighlighted(true);
@@ -591,7 +592,7 @@ void SetMenuReadyForTesting(bool ready) {
   // Two things can be installing simultaneously. When one starts or completes
   // the model builder will ask for the item to be highlighted.
   app_list::AppListItem* alternate_item_model =
-      model()->item_list()->item_at(0);
+      model()->top_level_item_list()->item_at(0);
   item_model->SetHighlighted(false);
   alternate_item_model->SetHighlighted(true);
   EXPECT_EQ(0u, [apps_grid_controller_ visiblePage]);
diff --git a/ui/app_list/test/app_list_test_model.cc b/ui/app_list/test/app_list_test_model.cc
index 357342acfd55c5..7a908127c40cab 100644
--- a/ui/app_list/test/app_list_test_model.cc
+++ b/ui/app_list/test/app_list_test_model.cc
@@ -64,7 +64,7 @@ std::string AppListTestModel::GetItemName(int id) {
 }
 
 void AppListTestModel::PopulateApps(int n) {
-  int start_index = static_cast<int>(item_list()->item_count());
+  int start_index = static_cast<int>(top_level_item_list()->item_count());
   for (int i = 0; i < n; ++i)
     CreateAndAddItem(GetItemName(start_index + i));
 }
@@ -75,10 +75,10 @@ void AppListTestModel::PopulateAppWithId(int id) {
 
 std::string AppListTestModel::GetModelContent() {
   std::string content;
-  for (size_t i = 0; i < item_list()->item_count(); ++i) {
+  for (size_t i = 0; i < top_level_item_list()->item_count(); ++i) {
     if (i > 0)
       content += ',';
-    content += item_list()->item_at(i)->id();
+    content += top_level_item_list()->item_at(i)->id();
   }
   return content;
 }
@@ -86,12 +86,14 @@ std::string AppListTestModel::GetModelContent() {
 AppListTestModel::AppListTestItem* AppListTestModel::CreateItem(
     const std::string& id) {
   AppListTestItem* item = new AppListTestItem(id, this);
-  size_t nitems = item_list()->item_count();
+  size_t nitems = top_level_item_list()->item_count();
   syncer::StringOrdinal position;
-  if (nitems == 0)
+  if (nitems == 0) {
     position = syncer::StringOrdinal::CreateInitialOrdinal();
-  else
-    position = item_list()->item_at(nitems - 1)->position().CreateAfter();
+  } else {
+    position =
+        top_level_item_list()->item_at(nitems - 1)->position().CreateAfter();
+  }
   item->SetPosition(position);
   SetItemName(item, id);
   return item;
@@ -104,7 +106,7 @@ AppListTestModel::AppListTestItem* AppListTestModel::CreateAndAddItem(
   return static_cast<AppListTestItem*>(item);
 }
 void AppListTestModel::HighlightItemAt(int index) {
-  AppListItem* item = item_list()->item_at(index);
+  AppListItem* item = top_level_item_list()->item_at(index);
   item->SetHighlighted(true);
 }
 
diff --git a/ui/app_list/views/app_list_folder_view.cc b/ui/app_list/views/app_list_folder_view.cc
index faeb59567e2bf6..8668622b14b682 100644
--- a/ui/app_list/views/app_list_folder_view.cc
+++ b/ui/app_list/views/app_list_folder_view.cc
@@ -71,11 +71,11 @@ AppListFolderView::AppListFolderView(AppsContainerView* container_view,
   SetFillsBoundsOpaquely(false);
 #endif
 
-  model_->item_list()->AddObserver(this);
+  model_->AddObserver(this);
 }
 
 AppListFolderView::~AppListFolderView() {
-  model_->item_list()->RemoveObserver(this);
+  model_->RemoveObserver(this);
   // Make sure |items_grid_view_| is deleted before |pagination_model_|.
   RemoveAllChildViews(true);
 }
@@ -129,7 +129,7 @@ bool AppListFolderView::OnKeyPressed(const ui::KeyEvent& event) {
   return items_grid_view_->OnKeyPressed(event);
 }
 
-void AppListFolderView::OnListItemRemoved(size_t index, AppListItem* item) {
+void AppListFolderView::OnAppListItemWillBeDeleted(AppListItem* item) {
   if (item == folder_item_) {
     items_grid_view_->OnFolderItemRemoved();
     folder_header_view_->OnFolderItemRemoved();
diff --git a/ui/app_list/views/app_list_folder_view.h b/ui/app_list/views/app_list_folder_view.h
index b58d5e4ee6a67f..95d4b2219be609 100644
--- a/ui/app_list/views/app_list_folder_view.h
+++ b/ui/app_list/views/app_list_folder_view.h
@@ -34,7 +34,7 @@ class PaginationModel;
 
 class AppListFolderView : public views::View,
                           public FolderHeaderViewDelegate,
-                          public AppListItemListObserver,
+                          public AppListModelObserver,
                           public ui::ImplicitAnimationObserver {
  public:
   AppListFolderView(AppsContainerView* container_view,
@@ -84,15 +84,15 @@ class AppListFolderView : public views::View,
   // Hides the view immediately without animation.
   void HideViewImmediately();
 
-  // views::View overrides:
+  // views::View
   virtual gfx::Size GetPreferredSize() OVERRIDE;
   virtual void Layout() OVERRIDE;
   virtual bool OnKeyPressed(const ui::KeyEvent& event) OVERRIDE;
 
-  // Overridden from AppListItemListObserver:
-  virtual void OnListItemRemoved(size_t index, AppListItem* item) OVERRIDE;
+  // AppListModelObserver
+  virtual void OnAppListItemWillBeDeleted(AppListItem* item) OVERRIDE;
 
-  // ui::ImplicitAnimationObserver overrides:
+  // ui::ImplicitAnimationObserver
   virtual void OnImplicitAnimationsCompleted() OVERRIDE;
 
   AppsGridView* items_grid_view() { return items_grid_view_; }
diff --git a/ui/app_list/views/app_list_main_view.cc b/ui/app_list/views/app_list_main_view.cc
index 850ca78ae398f0..f82236482d33fb 100644
--- a/ui/app_list/views/app_list_main_view.cc
+++ b/ui/app_list/views/app_list_main_view.cc
@@ -174,13 +174,13 @@ void AppListMainView::PreloadIcons(gfx::NativeView parent) {
 
   const int tiles_per_page = kPreferredCols * kPreferredRows;
   const int start_model_index = selected_page * tiles_per_page;
-  const int end_model_index = std::min(
-      static_cast<int>(model_->item_list()->item_count()),
-      start_model_index + tiles_per_page);
+  const int end_model_index =
+      std::min(static_cast<int>(model_->top_level_item_list()->item_count()),
+               start_model_index + tiles_per_page);
 
   pending_icon_loaders_.clear();
   for (int i = start_model_index; i < end_model_index; ++i) {
-    AppListItem* item = model_->item_list()->item_at(i);
+    AppListItem* item = model_->top_level_item_list()->item_at(i);
     if (item->icon().HasRepresentation(scale))
       continue;
 
diff --git a/ui/app_list/views/apps_container_view.cc b/ui/app_list/views/apps_container_view.cc
index 95ec3b74bc0449..66b774d9880d8e 100644
--- a/ui/app_list/views/apps_container_view.cc
+++ b/ui/app_list/views/apps_container_view.cc
@@ -51,7 +51,7 @@ AppsContainerView::AppsContainerView(AppListMainView* app_list_main_view,
   AddChildView(app_list_folder_view_);
 
   apps_grid_view_->SetModel(model_);
-  apps_grid_view_->SetItemList(model_->item_list());
+  apps_grid_view_->SetItemList(model_->top_level_item_list());
   SetShowState(SHOW_APPS,
                false);  /* show apps without animation */
 }
diff --git a/ui/app_list/views/apps_grid_view_unittest.cc b/ui/app_list/views/apps_grid_view_unittest.cc
index 5adacb1956f382..ed8898364862ca 100644
--- a/ui/app_list/views/apps_grid_view_unittest.cc
+++ b/ui/app_list/views/apps_grid_view_unittest.cc
@@ -110,7 +110,7 @@ class AppsGridViewTest : public views::ViewsTestBase {
     apps_grid_view_->SetLayout(kIconDimension, kCols, kRows);
     apps_grid_view_->SetBoundsRect(gfx::Rect(gfx::Size(kWidth, kHeight)));
     apps_grid_view_->SetModel(model_.get());
-    apps_grid_view_->SetItemList(model_->item_list());
+    apps_grid_view_->SetItemList(model_->top_level_item_list());
 
     test_api_.reset(new AppsGridViewTestApi(apps_grid_view_.get()));
   }
@@ -126,7 +126,7 @@ class AppsGridViewTest : public views::ViewsTestBase {
   }
 
   AppListItemView* GetItemViewForPoint(const gfx::Point& point) {
-    for (size_t i = 0; i < model_->item_list()->item_count(); ++i) {
+    for (size_t i = 0; i < model_->top_level_item_list()->item_count(); ++i) {
       AppListItemView* view = GetItemViewAt(i);
       if (view->bounds().Contains(point))
         return view;
@@ -135,7 +135,7 @@ class AppsGridViewTest : public views::ViewsTestBase {
   }
 
   gfx::Rect GetItemTileRectAt(int row, int col) {
-    DCHECK_GT(model_->item_list()->item_count(), 0u);
+    DCHECK_GT(model_->top_level_item_list()->item_count(), 0u);
 
     gfx::Insets insets(apps_grid_view_->GetInsets());
     gfx::Rect rect(gfx::Point(insets.left(), insets.top()),
@@ -208,7 +208,7 @@ TEST_F(AppsGridViewTest, EnsureHighlightedVisible) {
   EXPECT_EQ(1, pagination_model_->selected_page());
 
   // Highlight last one in the model and last page should be selected.
-  model_->HighlightItemAt(model_->item_list()->item_count() - 1);
+  model_->HighlightItemAt(model_->top_level_item_list()->item_count() - 1);
   EXPECT_EQ(kPages - 1, pagination_model_->selected_page());
 }