Refactor accessible focus ring code so the layers are animation observers.

chrome/browser/chromeos/ui/focus_ring_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 CHROME_BROWSER_CHROMEOS_UI_FOCUS_RING_CONTROLLER_H_
 #define CHROME_BROWSER_CHROMEOS_UI_FOCUS_RING_CONTROLLER_H_
 
 #include <memory>
 
 #include "base/macros.h"
@@ skipping 19 matching lines @@
  public:
   FocusRingController();
   ~FocusRingController() override;
 
   // Turns on/off the focus ring.
   void SetVisible(bool visible);
 
  private:
   // FocusRingLayerDelegate.
   void OnDeviceScaleFactorChanged() override;
+  void OnAnimationStep(base::TimeTicks timestamp) override;
 
   // Sets the focused |widget|.
   void SetWidget(views::Widget* widget);
 
   // Updates the focus ring to the focused view of |widget_|. If |widget_| is
   // NULL or has no focused view, removes the focus ring. Otherwise, draws it.
   void UpdateFocusRing();
 
   // views::WidgetObserver overrides:
   void OnWidgetDestroying(views::Widget* widget) override;
@@ skipping 13 matching lines @@
 
   views::Widget* widget_;
   std::unique_ptr<FocusRingLayer> focus_ring_layer_;
 
   DISALLOW_COPY_AND_ASSIGN(FocusRingController);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_UI_FOCUS_RING_CONTROLLER_H_