CrOS: Fix two-finger touch on shelf app icons

The bug is that after two-finger tapping on an app icon in
the shelf, the shelf sometimes becomes unresponsive.

This was caused by logic that assumed we wanted to forward all
gesture events when the context menu was created with a gesture event.

This is fixed by adding a check to see if we are actually dragging
an app icon before asking MenuRunner to send events to owner.

TEST=manual

Bug: 794681
Change-Id: Ib2b764126874f9fd58578a1610a70e2c7881ff78
Reviewed-on: https://chromium-review.googlesource.com/828293
Commit-Queue: Alex Newcomer <newcomer@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524502}

ash/shelf/shelf_view.cc

@@ -202,6 +202,24 @@ int64_t GetDisplayIdForView(View* view) {
   return display::Screen::GetScreen()->GetDisplayNearestWindow(window).id();
 }
 
+// Whether |item_view| is a ShelfButton and its state is STATE_DRAGGING.
+bool ShelfButtonIsInDrag(const ShelfItemType item_type,
+                         const views::View* item_view) {
+  switch (item_type) {
+    case TYPE_PINNED_APP:
+    case TYPE_BROWSER_SHORTCUT:
+    case TYPE_APP:
+      return static_cast<const ShelfButton*>(item_view)->state() &
+             ShelfButton::STATE_DRAGGING;
+    case TYPE_DIALOG:
+    case TYPE_APP_PANEL:
+    case TYPE_BACK_BUTTON:
+    case TYPE_APP_LIST:
+    case TYPE_UNDEFINED:
+      return false;
+  }
+}
+
 }  // namespace
 
 // AnimationDelegate used when deleting an item. This steadily decreased the
@@ -1861,8 +1879,7 @@ void ShelfView::ShowMenu(std::unique_ptr<ui::MenuModel> menu_model,
 
   // Only selected shelf items with context menu opened can be dragged.
   const ShelfItem* item = ShelfItemForView(source);
-  if (context_menu && item && item->type != TYPE_APP_LIST &&
-      item->type != TYPE_BACK_BUTTON &&
+  if (context_menu && item && ShelfButtonIsInDrag(item->type, source) &&
       source_type == ui::MenuSourceType::MENU_SOURCE_TOUCH) {
     run_types |= views::MenuRunner::SEND_GESTURE_EVENTS_TO_OWNER;
   }