Adds UMA for screen rotation animation smoothness.

ash/rotator/screen_rotation_animator.h

 // Copyright 2015 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_ROTATOR_SCREEN_ROTATION_ANIMATOR_H_
 #define ASH_ROTATOR_SCREEN_ROTATION_ANIMATOR_H_
 
 #include <stdint.h>
 
 #include "ash/ash_export.h"
@@ skipping 38 matching lines @@
   void RemoveScreenRotationAnimatorObserver(
       ScreenRotationAnimatorObserver* observer);
 
   void OnLayerAnimationEnded();
 
   void OnLayerAnimationAborted();
 
  private:
   friend class ash::test::ScreenRotationAnimatorTestApi;
   struct ScreenRotationRequest;
+  class ScreenRotationAnimationMetricsReporter;
 
   // Set the screen orientation to |new_rotation| and animate the change. The
   // animation will rotate the initial orientation's layer towards the new
   // orientation through |rotation_degrees| while fading out, and the new
   // orientation's layer will be rotated in to the |new_orientation| through
   // |rotation_degrees| arc.
   void AnimateRotation(std::unique_ptr<ScreenRotationRequest> rotation_request);
 
   // When screen rotation animation is ended or aborted, if the request queue is
   // not empty, it will call |Rotate()| with the pending rotation request.
   // Otherwise it will notify |screen_rotation_animator_observer_|.
   void ProcessAnimationQueue();
 
   void set_disable_animation_timers_for_test(bool disable_timers);
 
   void StopAnimating();
 
   // The id of the display to rotate.
   int64_t display_id_;
   bool is_rotating_;
   // Only set in unittest to disable animation timers.
   bool disable_animation_timers_for_test_;
   base::ObserverList<ScreenRotationAnimatorObserver>
       screen_rotation_animator_observers_;
   std::unique_ptr<ui::LayerTreeOwner> old_layer_tree_owner_;
   std::unique_ptr<ScreenRotationRequest> last_pending_request_;
+  std::unique_ptr<ScreenRotationAnimationMetricsReporter> metrics_reporter_;
   base::WeakPtrFactory<ScreenRotationAnimator> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ScreenRotationAnimator);
 };
 
 }  // namespace ash
 
 #endif  // ASH_ROTATOR_SCREEN_ROTATION_ANIMATOR_H_