Reland of "Apply Shelf/Dock opacity animations for the Material Design style."

ash/common/shelf/app_list_button.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef ASH_COMMON_SHELF_APP_LIST_BUTTON_H_
 #define ASH_COMMON_SHELF_APP_LIST_BUTTON_H_
 
 #include "ash/ash_export.h"
 #include "base/macros.h"
 #include "ui/views/controls/button/image_button.h"
 
 namespace ash {
 class InkDropButtonListener;
 class ShelfView;
 class WmShelf;
 
 // Button used for the AppList icon on the shelf.
 class ASH_EXPORT AppListButton : public views::ImageButton {
  public:
   AppListButton(InkDropButtonListener* listener,
                 ShelfView* shelf_view,
                 WmShelf* wm_shelf);
   ~AppListButton() override;
 
   void OnAppListShown();
   void OnAppListDismissed();
 
   bool draw_background_as_active() { return draw_background_as_active_; }
 
+  // Sets alpha value of the background and schedules a paint.
+  void SetBackgroundAlpha(int alpha);
+
  protected:
   // views::ImageButton overrides:
   bool OnMousePressed(const ui::MouseEvent& event) override;
   void OnMouseReleased(const ui::MouseEvent& event) override;
   void OnMouseCaptureLost() override;
   bool OnMouseDragged(const ui::MouseEvent& event) override;
   void OnPaint(gfx::Canvas* canvas) override;
   void GetAccessibleState(ui::AXViewState* state) override;
   std::unique_ptr<views::InkDropRipple> CreateInkDropRipple() const override;
   void NotifyClick(const ui::Event& event) override;
@@ skipping 14 matching lines @@
                          const gfx::ImageSkia& foreground_image);
 
   // Helper function to paint the AppList button in Chrome OS non-MD.
   void PaintAppListButton(gfx::Canvas* canvas,
                           const gfx::ImageSkia& foreground_image);
 
   // True if the background should render as active, regardless of the state of
   // the application list.
   bool draw_background_as_active_;
 
+  // Alpha value used to paint the background.
+  int background_alpha_;
+
   InkDropButtonListener* listener_;
   ShelfView* shelf_view_;
   WmShelf* wm_shelf_;
 
   DISALLOW_COPY_AND_ASSIGN(AppListButton);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_SHELF_APP_LIST_BUTTON_H_