cros: Fix crash on multiprofile switch

If the profile being left had a folder, we kept a reference to that
folder in AppListModel's ScopedObserverList.

But when profiles  are swapped, we delete everything in the
AppListModel::top_level_item_list_. This means the folder is deleted.

Remove the item from the ScopedObserverList if it is a folder.

Bug: 1130901
Change-Id: I1d6ab268739f81904debcc4654e5663ddf768013
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2464151
Commit-Queue: Alex Newcomer <newcomer@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816300}

ash/app_list/app_list_controller_impl_unittest.cc

@@ -651,6 +651,29 @@ TEST_F(AppListControllerImplTest,
   EXPECT_FALSE(GetAppListView()->GetWidget()->GetNativeWindow()->IsVisible());
 }
 
+// Tests that swapping out an AppListModel (simulating a profile swap with
+// multiprofile enabled) drops all references to previous folders (see
+// https://crbug.com/1130901).
+TEST_F(AppListControllerImplTest, SimulateProfileSwapNoCrashOnDestruct) {
+  // Add a folder, whose AppListItemList the AppListModel will observe.
+  const std::string folder_id("folder_1");
+  auto folder = std::make_unique<AppListFolderItem>(folder_id);
+  AppListModel* model = Shell::Get()->app_list_controller()->GetModel();
+  model->AddItem(std::move(folder));
+
+  for (int i = 0; i < 2; ++i) {
+    auto item = std::make_unique<AppListItem>(base::StringPrintf("app_%d", i));
+    model->AddItemToFolder(std::move(item), folder_id);
+  }
+
+  // Set a new model, simulating profile switching in multi-profile mode. This
+  // should cleanly drop the reference to the folder added earlier.
+  Shell::Get()->app_list_controller()->SetModelData(
+      /*profile_id=*/12, /*apps=*/{}, /*is_search_engine_google=*/false);
+
+  // Test that there is no crash on ~AppListModel() when the test finishes.
+}
+
 class AppListControllerImplTestWithNotificationBadging
     : public AppListControllerImplTest {
  public:

ash/app_list/model/app_list_model.cc

@@ -302,6 +302,10 @@ void AppListModel::DeleteAllItems() {
     const std::string id = item->id();
     for (auto& observer : observers_)
       observer.OnAppListItemWillBeDeleted(item);
+    if (item->GetItemType() == AppListFolderItem::kItemType) {
+      item_list_scoped_observer_.Remove(
+          static_cast<AppListFolderItem*>(item)->item_list());
+    }
     top_level_item_list_->DeleteItemAt(0);
     for (auto& observer : observers_)
       observer.OnAppListItemDeleted(id);