Reduce layers in overview mode

* Change ShieldWidget's layer to NOW_DRAWN because it's always transparent.
* Remove layer on image_view/title_view
* Create an layer for unsnappable lable on demand.

Bug: 897870
Test: no functional change. Updated the unit test.
Change-Id: I23093ade07bc943ad16572d2704b78b13883c3bd
Reviewed-on: https://chromium-review.googlesource.com/c/1295335
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601859}

ash/wm/overview/overview_utils.cc

@@ -209,7 +209,7 @@ std::unique_ptr<views::Widget> CreateBackgroundWidget(aura::Window* root_window,
   wm::GetWindowState(widget_window)->set_ignored_by_shelf(true);
   if (params.layer_type == ui::LAYER_SOLID_COLOR) {
     widget_window->layer()->SetColor(background_color);
-  } else {
+  } else if (params.layer_type == ui::LAYER_TEXTURED) {
     views::View* content_view = new views::View();
     content_view->SetBackground(std::make_unique<BackgroundWith1PxBorder>(
         background_color, border_color, border_thickness, border_radius));

ash/wm/overview/window_grid.cc

@@ -1091,7 +1091,7 @@ void WindowGrid::InitShieldWidget() {
           ? 1.f
           : 0.f;
   shield_widget_ = CreateBackgroundWidget(
-      root_window_, ui::LAYER_SOLID_COLOR, SK_ColorTRANSPARENT, 0, 0,
+      root_window_, ui::LAYER_NOT_DRAWN, SK_ColorTRANSPARENT, 0, 0,
       SK_ColorTRANSPARENT, initial_opacity, /*parent=*/nullptr,
       /*stack_on_top=*/true);
   aura::Window* widget_window = shield_widget_->GetNativeWindow();

ash/wm/overview/window_selector_item.cc

@@ -316,38 +316,44 @@ class WindowSelectorItem::CaptionContainerView : public views::View {
         close_button_(close_button) {
     AddChildView(listener_button_);
 
-    // Helper function to add a child view to a parent view and make it paint to
-    // layer.
-    auto add_child_with_layer = [](views::View* parent, views::View* child) {
-      child->SetPaintToLayer();
-      child->layer()->SetFillsBoundsOpaquely(false);
-      parent->AddChildView(child);
-    };
-
     header_view_ = new views::View();
     views::BoxLayout* layout =
         header_view_->SetLayoutManager(std::make_unique<views::BoxLayout>(
             views::BoxLayout::kHorizontal, gfx::Insets(),
             kHorizontalLabelPaddingDp));
     if (image_view_)
-      add_child_with_layer(header_view_, image_view_);
-    add_child_with_layer(header_view_, title_label_);
-    add_child_with_layer(header_view_, close_button_);
-    add_child_with_layer(this, header_view_);
+      header_view_->AddChildView(image_view_);
+    header_view_->AddChildView(title_label_);
+    AddChildWithLayer(header_view_, close_button_);
+    AddChildWithLayer(this, header_view_);
     layout->SetFlexForView(title_label_, 1);
+  }
 
+  ~CaptionContainerView() override {
+    // If the cannot snap container was never created, delete cannot_snap_label_
+    // manually.
+    if (!cannot_snap_container_)
+      delete cannot_snap_label_;
+  }
+
+  RoundedRectView* GetCannotSnapContainer() {
+    if (!cannot_snap_container_) {
       // Use |cannot_snap_container_| to specify the padding surrounding
       // |cannot_snap_label_| and to give the label rounded corners.
       cannot_snap_container_ = new RoundedRectView(
           kSplitviewLabelRoundRectRadiusDp, kSplitviewLabelBackgroundColor);
-    cannot_snap_container_->SetLayoutManager(std::make_unique<views::BoxLayout>(
+      cannot_snap_container_->SetLayoutManager(
+          std::make_unique<views::BoxLayout>(
               views::BoxLayout::kVertical,
               gfx::Insets(kSplitviewLabelVerticalInsetDp,
                           kSplitviewLabelHorizontalInsetDp)));
       cannot_snap_container_->AddChildView(cannot_snap_label_);
       cannot_snap_container_->set_can_process_events_within_subtree(false);
-    add_child_with_layer(this, cannot_snap_container_);
+      AddChildWithLayer(this, cannot_snap_container_);
       cannot_snap_container_->layer()->SetOpacity(0.f);
+      Layout();
+    }
+    return cannot_snap_container_;
   }
 
   ShieldButton* listener_button() { return listener_button_; }
@@ -370,8 +376,11 @@ class WindowSelectorItem::CaptionContainerView : public views::View {
   }
 
   void SetCannotSnapLabelVisibility(bool visible) {
+    if (!cannot_snap_container_ && !visible)
+      return;
+
     DoSplitviewOpacityAnimation(
-        cannot_snap_container_->layer(),
+        GetCannotSnapContainer()->layer(),
         visible ? SPLITVIEW_ANIMATION_SELECTOR_ITEM_FADE_IN
                 : SPLITVIEW_ANIMATION_SELECTOR_ITEM_FADE_OUT);
   }
@@ -399,12 +408,14 @@ class WindowSelectorItem::CaptionContainerView : public views::View {
     backdrop_bounds_ = bounds;
     backdrop_bounds_.Inset(0, visible_height, 0, 0);
 
+    if (cannot_snap_container_) {
       // Position the cannot snap label in the middle of the item, minus the
       // title.
       gfx::Rect cannot_snap_bounds = GetLocalBounds();
       cannot_snap_bounds.Inset(0, visible_height, 0, 0);
       cannot_snap_bounds.ClampToCenteredSize(label_size);
       cannot_snap_container_->SetBoundsRect(cannot_snap_bounds);
+    }
 
     // Position the header at the top. The left should be indented to match
     // the transformed window, but not the right because the close button hit
@@ -446,11 +457,19 @@ class WindowSelectorItem::CaptionContainerView : public views::View {
     }
   }
 
+  // Helper function to add a child view to a parent view and make it paint to
+  // layer.
+  static void AddChildWithLayer(views::View* parent, views::View* child) {
+    child->SetPaintToLayer();
+    child->layer()->SetFillsBoundsOpaquely(false);
+    parent->AddChildView(child);
+  };
+
   ShieldButton* listener_button_;
   views::ImageView* image_view_;
   views::Label* title_label_;
   views::Label* cannot_snap_label_;
-  RoundedRectView* cannot_snap_container_;
+  RoundedRectView* cannot_snap_container_ = nullptr;
   views::ImageButton* close_button_;
   // View which contains the icon, title and close button.
   views::View* header_view_ = nullptr;

ash/wm/overview/window_selector_unittest.cc

@@ -4461,25 +4461,29 @@ TEST_F(SplitViewWindowSelectorTest, OverviewUnsnappableIndicatorVisibility) {
   WindowSelectorItem* unsnappable_selector_item =
       GetWindowItemForWindow(grid_index, unsnappable_window.get());
 
-  // Note: Check opacities of  |cannot_snap_label_view_|'s parent (which handles
-  // the padding and rounded corners) is actually the item whose layer's opacity
-  // gets altered.
-  ui::Layer* snappable_layer =
-      snappable_selector_item->cannot_snap_label_view_->parent()->layer();
-  ui::Layer* unsnappable_layer =
-      unsnappable_selector_item->cannot_snap_label_view_->parent()->layer();
-  ASSERT_TRUE(snappable_layer);
-  ASSERT_TRUE(unsnappable_layer);
-
-  EXPECT_EQ(0.f, snappable_layer->opacity());
-  EXPECT_EQ(0.f, unsnappable_layer->opacity());
+  // Note: the container for |cannot_snap_label_view_| will be created
+  // on demand, and its parent remains null until the container is created.
+  EXPECT_FALSE(snappable_selector_item->cannot_snap_label_view_->parent());
+  ASSERT_FALSE(unsnappable_selector_item->cannot_snap_label_view_->parent());
 
   // Snap the extra snappable window to enter split view mode.
   split_view_controller()->SnapWindow(window1.get(), SplitViewController::LEFT);
   ASSERT_TRUE(split_view_controller()->IsSplitViewModeActive());
-
-  EXPECT_EQ(0.f, snappable_layer->opacity());
+  EXPECT_FALSE(snappable_selector_item->cannot_snap_label_view_->parent());
+  ASSERT_TRUE(unsnappable_selector_item->cannot_snap_label_view_->parent());
+  ui::Layer* unsnappable_layer =
+      unsnappable_selector_item->cannot_snap_label_view_->parent()->layer();
   EXPECT_EQ(1.f, unsnappable_layer->opacity());
+
+  // Exiting the splitview will hide the unsnappable label.
+  const gfx::Rect divider_bounds =
+      GetSplitViewDividerBounds(/*is_dragging=*/false);
+  ui::test::EventGenerator* generator = GetEventGenerator();
+  generator->set_current_location(divider_bounds.CenterPoint());
+  generator->DragMouseTo(0, 0);
+
+  EXPECT_FALSE(split_view_controller()->IsSplitViewModeActive());
+  EXPECT_EQ(0.f, unsnappable_layer->opacity());
 }
 
 // Test that when splitview mode and overview mode are both active at the same