Standardize usage of virtual/override/final specifiers.

ash/shelf/background_animator.h

Index: ash/shelf/background_animator.h
diff --git a/ash/shelf/background_animator.h b/ash/shelf/background_animator.h
index ec5f6f380906e93970b5da492d68d19b97b8967b..4c01ac15c09e2ce7c9c7c9252d9480321551354a 100644
--- a/ash/shelf/background_animator.h
+++ b/ash/shelf/background_animator.h
@@ -33,7 +33,7 @@ class ASH_EXPORT BackgroundAnimator : public gfx::AnimationDelegate {
   BackgroundAnimator(BackgroundAnimatorDelegate* delegate,
                      int min_alpha,
                      int max_alpha);
-  virtual ~BackgroundAnimator();
+  ~BackgroundAnimator() override;
 
   // Sets the transition time in ms.
   void SetDuration(int time_in_ms);
@@ -48,7 +48,7 @@ class ASH_EXPORT BackgroundAnimator : public gfx::AnimationDelegate {
   int alpha() const { return alpha_; }
 
   // gfx::AnimationDelegate overrides:
-  virtual void AnimationProgressed(const gfx::Animation* animation) override;
+  void AnimationProgressed(const gfx::Animation* animation) override;
 
  private:
   BackgroundAnimatorDelegate* delegate_;