Add ink drop ripple to overview mode button

ash/common/wm/overview/window_selector_controller.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_WM_OVERVIEW_WINDOW_SELECTOR_CONTROLLER_H_
 #define ASH_COMMON_WM_OVERVIEW_WINDOW_SELECTOR_CONTROLLER_H_
 
 #include <list>
 #include <memory>
 #include <vector>
@@ skipping 12 matching lines @@
 // allows selecting a window to activate it.
 class ASH_EXPORT WindowSelectorController : public WindowSelectorDelegate {
  public:
   WindowSelectorController();
   ~WindowSelectorController() override;
 
   // Returns true if selecting windows in an overview is enabled. This is false
   // at certain times, such as when the lock screen is visible.
   static bool CanSelect();
 
-  // Enters overview mode. This is essentially the window cycling mode however
-  // not released on releasing the alt key and allows selecting with the mouse
-  // or touch rather than keypresses.
-  void ToggleOverview();
+  // Attempts to toggle overview mode and returns true if successful (showing
+  // overview would be unsuccessful if there are no windows to show).
+  bool ToggleOverview();
 
   // Returns true if window selection mode is active.
   bool IsSelecting() const;
 
   // Returns true if overview mode is restoring minimized windows so that they
   // are visible during overview mode.
   bool IsRestoringMinimizedWindows() const;
 
   // WindowSelectorDelegate:
   void OnSelectionEnded() override;
@@ skipping 15 matching lines @@
   std::vector<std::unique_ptr<DelayedAnimationObserver>> delayed_animations_;
   std::unique_ptr<WindowSelector> window_selector_;
   base::Time last_selection_time_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowSelectorController);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_WM_OVERVIEW_WINDOW_SELECTOR_CONTROLLER_H_