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

ash/common/shelf/overflow_button.h

 // Copyright 2013 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_OVERFLOW_BUTTON_H_
 #define ASH_COMMON_SHELF_OVERFLOW_BUTTON_H_
 
 #include "base/macros.h"
 #include "ui/gfx/image/image_skia.h"
 #include "ui/views/controls/button/custom_button.h"
 
 namespace ash {
 class InkDropButtonListener;
 class WmShelf;
 
 // Shelf overflow chevron button.
 class OverflowButton : public views::CustomButton {
  public:
   OverflowButton(InkDropButtonListener* listener, WmShelf* wm_shelf);
   ~OverflowButton() override;
 
   void OnShelfAlignmentChanged();
 
+  // Sets alpha value of the background and schedules a paint.
+  void SetBackgroundAlpha(int alpha);
+
  private:
   // views::View:
   void OnPaint(gfx::Canvas* canvas) override;
 
   // views::CustomButton:
   void NotifyClick(const ui::Event& event) override;
 
   // Helper functions to paint the background and foreground of the button
   // at |bounds|.
   void PaintBackground(gfx::Canvas* canvas, const gfx::Rect& bounds);
@@ skipping 17 matching lines @@
   gfx::ImageSkia bottom_image_md_;
 
   // Cached rotations of |bottom_image_| used for left and right shelf
   // alignments.
   gfx::ImageSkia left_image_;
   gfx::ImageSkia right_image_;
 
   InkDropButtonListener* listener_;
   WmShelf* wm_shelf_;
 
+  // Alpha value used to paint the background.
+  int background_alpha_;
+
   DISALLOW_COPY_AND_ASSIGN(OverflowButton);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_SHELF_OVERFLOW_BUTTON_H_