Destroy layers of items which are not in the current page

Currently UpdateOpacity() assumes the correspondance for the item
and the page doesn't change during the drag. When it happens, some
items remain painting to layer with lower opacity after the dragging
of app-list is done. This leads to invisibility of some app list
which isn't in the current page. I think this is the reason for
the reported issue.

Bug: 990529
Test: the new test case in ash_unittests
Change-Id: I046cdfa62f4305f70a38859a2b71534d016c60ce
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1736177
Commit-Queue: Jun Mukai <mukai@chromium.org>
Reviewed-by: Alex Newcomer <newcomer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#684150}

ash/app_list/app_list_presenter_delegate_unittest.cc

@@ -1516,6 +1516,84 @@ TEST_F(AppListPresenterDelegateHomeLauncherTest, MouseDragAppListItemOpacity) {
   }
 }
 
+// Tests that ending of the mouse dragging of app-list destroys the layers for
+// the items which are in the second page. See https://crbug.com/990529.
+TEST_F(AppListPresenterDelegateHomeLauncherTest, LayerOnSecondPage) {
+  const int items_in_page =
+      app_list::AppListConfig::instance().preferred_cols() *
+      app_list::AppListConfig::instance().preferred_rows();
+  app_list::AppListModel* model =
+      Shell::Get()->app_list_controller()->GetModel();
+  for (int i = 0; i < items_in_page; ++i) {
+    std::unique_ptr<app_list::AppListItem> item(
+        new app_list::AppListItem(base::StringPrintf("fake id %02d", i)));
+    model->AddItem(std::move(item));
+  }
+
+  GetAppListTestHelper()->ShowAndRunLoop(GetPrimaryDisplayId());
+  GetAppListTestHelper()->CheckState(AppListViewState::kPeeking);
+
+  const gfx::Point start_point = GetAppListView()->GetBoundsInScreen().origin();
+  ui::test::EventGenerator* generator = GetEventGenerator();
+  generator->MoveMouseTo(start_point);
+  generator->PressLeftButton();
+  app_list::AppsGridView* apps_grid_view = GetAppListView()
+                                               ->app_list_main_view()
+                                               ->contents_view()
+                                               ->GetAppsContainerView()
+                                               ->apps_grid_view();
+
+  // Drags the mouse a bit above (twice as shelf's height). This should show the
+  // item vaguely.
+  const int shelf_height =
+      GetPrimaryShelf()->GetShelfViewForTesting()->height();
+  generator->MoveMouseBy(0, -shelf_height * 2);
+  // All of the item should have the layer at this point.
+  for (int i = 0; i < items_in_page; ++i) {
+    views::View* item_view = apps_grid_view->view_model()->view_at(i);
+    EXPECT_TRUE(item_view->layer()) << "at " << i;
+    EXPECT_LE(0.f, item_view->layer()->opacity()) << "at " << i;
+    EXPECT_GE(1.f, item_view->layer()->opacity()) << "at " << i;
+  }
+
+  // Add items at the front of the items.
+  const int additional_items = 10;
+  syncer::StringOrdinal prev_position =
+      model->top_level_item_list()->item_at(0)->position();
+  for (int i = 0; i < additional_items; ++i) {
+    std::unique_ptr<app_list::AppListItem> item(new app_list::AppListItem(
+        base::StringPrintf("fake id %02d", i + items_in_page)));
+    // Update the position so that the item is added at the front of the list.
+    auto metadata = item->CloneMetadata();
+    metadata->position = prev_position.CreateBefore();
+    prev_position = metadata->position;
+    item->SetMetadata(std::move(metadata));
+    model->AddItem(std::move(item));
+  }
+
+  generator->MoveMouseBy(0, -1);
+
+  // At this point, some items move out from the first page.
+  EXPECT_LT(1, apps_grid_view->pagination_model()->total_pages());
+
+  // The items on the first page should have layers.
+  for (int i = 0; i < items_in_page; ++i) {
+    views::View* item_view = apps_grid_view->view_model()->view_at(i);
+    EXPECT_TRUE(item_view->layer()) << "at " << i;
+    EXPECT_LE(0.f, item_view->layer()->opacity()) << "at " << i;
+    EXPECT_GE(1.f, item_view->layer()->opacity()) << "at " << i;
+  }
+
+  // Drag to the top of the screen and finish the drag. It should destroy all
+  // of the layers, including items on the second page.
+  generator->MoveMouseTo(start_point.x(), 0);
+  generator->ReleaseLeftButton();
+  for (int i = 0; i < apps_grid_view->view_model()->view_size(); ++i) {
+    views::View* item_view = apps_grid_view->view_model()->view_at(i);
+    EXPECT_FALSE(item_view->layer()) << "at " << i;
+  }
+}
+
 // Tests that the app list is shown automatically when the tablet mode is on.
 // The app list is dismissed when the tablet mode is off.
 TEST_F(AppListPresenterDelegateHomeLauncherTest, ShowAppListForTabletMode) {

ash/app_list/views/apps_grid_view.cc

@@ -1982,9 +1982,11 @@ void AppsGridView::UpdateOpacity() {
   // view (i.e. this class).
   if (should_restore_opacity) {
     // Layers are not necessary. Destroy them, and return. No need to update
-    // opacity.
-    for (size_t i = 0; i < current_page.size(); ++i)
-      current_page[i]->DestroyLayer();
+    // opacity. This needs to be done on all views within |view_model_| because
+    // some item view might have been moved out from the current page. See also
+    // https://crbug.com/990529.
+    for (int i = 0; i < view_model_.view_size(); ++i)
+      view_model_.view_at(i)->DestroyLayer();
     return;
   }