desk_templates: Fix crash when shut down DesksTemplatesPresenter.

The DesksClient shuts down before Shell, making the model unusable
during Shell shutdown. This adds a observer to check when the model is
destroying, to give observers a chance to remove themselves.

Fixed: 1258979
Test: manual
Change-Id: Iee5e22485c180c09511ac4da4105f9f8f0e73985
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3218653
Reviewed-by: Colin Blundell <blundell@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/main@{#931088}

ash/wm/desks/templates/desks_templates_presenter.cc

@@ -44,6 +44,10 @@ DesksTemplatesPresenter::DesksTemplatesPresenter(
 
 DesksTemplatesPresenter::~DesksTemplatesPresenter() = default;
 
+void DesksTemplatesPresenter::OnDeskModelDestroying() {
+  desk_model_observation_.Reset();
+}
+
 void DesksTemplatesPresenter::OnGetAllEntries(
     desks_storage::DeskModel::GetAllEntriesStatus status,
     std::vector<DeskTemplate*> entries) {

ash/wm/desks/templates/desks_templates_presenter.h

@@ -34,6 +34,7 @@ class ASH_EXPORT DesksTemplatesPresenter : desks_storage::DeskModelObserver {
   // TODO(sammiequon): Implement these once the model starts sending these
   // messages.
   void DeskModelLoaded() override {}
+  void OnDeskModelDestroying() override;
   void EntriesAddedOrUpdatedRemotely(
       const std::vector<const ash::DeskTemplate*>& new_entries) override {}
   void EntriesRemovedRemotely(const std::vector<std::string>& uuids) override {}

components/desks_storage/core/desk_model.cc

@@ -14,7 +14,10 @@ namespace desks_storage {
 
 DeskModel::DeskModel() = default;
 
-DeskModel::~DeskModel() = default;
+DeskModel::~DeskModel() {
+  for (DeskModelObserver& observer : observers_)
+    observer.OnDeskModelDestroying();
+}
 
 void DeskModel::AddObserver(DeskModelObserver* observer) {
   DCHECK(observer);
@@ -42,4 +45,4 @@ void DeskModel::SetPolicyDeskTemplates(const std::string& policyJson) {
   }
 }
 
-}  // namespace desks_storage
+}  // namespace desks_storage

components/desks_storage/core/desk_model_observer.h

@@ -26,6 +26,11 @@ class DeskModelObserver {
   // is unsafe to use the model.
   virtual void DeskModelLoaded() = 0;
 
+  // Invoked when the model is about to be destroyed. Gives observes which may
+  // outlive the model a chance to stop observing. Not pure virtual because it
+  // needs to be called from the destructor.
+  virtual void OnDeskModelDestroying() {}
+
   // Invoked when desk templates are added/updated, removed remotely via sync.
   // This is the mechanism for the sync server to push changes in the state of
   // the model to clients.
@@ -45,4 +50,4 @@ class DeskModelObserver {
 
 }  // namespace desks_storage
 
-#endif  // COMPONENTS_DESKS_STORAGE_CORE_DESK_MODEL_OBSERVER_H_
+#endif  // COMPONENTS_DESKS_STORAGE_CORE_DESK_MODEL_OBSERVER_H_

components/desks_storage/core/desk_sync_bridge_unittest.cc

@@ -953,4 +953,4 @@ TEST_F(DeskSyncBridgeTest, MergeSyncDataUploadsLocalOnlyEntries) {
 
 }  // namespace
 
-}  // namespace desks_storage
+}  // namespace desks_storage