Draggable peeking/fullscreen launcher with transparent background.

ash/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_SHELF_APP_LIST_BUTTON_H_
 #define ASH_SHELF_APP_LIST_BUTTON_H_
 
 #include <memory>
 
 #include "ash/ash_export.h"
+#include "ash/shell_observer.h"
 #include "base/macros.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/views/controls/button/image_button.h"
 
 namespace ash {
 class InkDropButtonListener;
 class Shelf;
 class ShelfView;
 
 // Button used for the AppList icon on the shelf.
-class ASH_EXPORT AppListButton : public views::ImageButton {
+class ASH_EXPORT AppListButton : public views::ImageButton,
+                                 public ShellObserver {
  public:
   AppListButton(InkDropButtonListener* listener,
                 ShelfView* shelf_view,
                 Shelf* shelf);
   ~AppListButton() override;
 
   void OnAppListShown();
   void OnAppListDismissed();
 
   bool is_showing_app_list() const { return is_showing_app_list_; }
@@ skipping 16 matching lines @@
   bool ShouldEnterPushedState(const ui::Event& event) override;
   std::unique_ptr<views::InkDrop> CreateInkDrop() override;
   std::unique_ptr<views::InkDropMask> CreateInkDropMask() const override;
   void PaintButtonContents(gfx::Canvas* canvas) override;
 
  private:
   // Get the center point of the app list button used to draw its background and
   // ink drops.
   gfx::Point GetCenterPoint() const;
 
+  // ShellObserver overrides:
+  void OnAppListVisibilityChanged(bool shown,
+                                  aura::Window* root_window) override;
+
   // True if the app list is currently showing for this display.
   // This is useful because other IsApplistVisible functions aren't per-display.
   bool is_showing_app_list_;
 
   // Color used to paint the background.
   SkColor background_color_;
 
   InkDropButtonListener* listener_;
   ShelfView* shelf_view_;
   Shelf* shelf_;
 
   DISALLOW_COPY_AND_ASSIGN(AppListButton);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SHELF_APP_LIST_BUTTON_H_