[animations] Adds metrics for jank on selected layer animations

ui/compositor/layer_animator.h

Index: ui/compositor/layer_animator.h
diff --git a/ui/compositor/layer_animator.h b/ui/compositor/layer_animator.h
index f730adce1773be184c5999d53c82a68fd81670d8..e027ddab55579ae5c3bc242309953da5cef38738 100644
--- a/ui/compositor/layer_animator.h
+++ b/ui/compositor/layer_animator.h
@@ -362,6 +362,10 @@ class COMPOSITOR_EXPORT LayerAnimator
   void AttachLayerToAnimationPlayer(int layer_id);
   void DetachLayerFromAnimationPlayer();
 
+  void set_animation_metrics_reporter(AnimationMetricsReporter* reporter) {
+    animation_metrics_reporter_ = reporter;
+  }
+
   // This is the queue of animations to run.
   AnimationQueue animation_queue_;
 
@@ -401,6 +405,9 @@ class COMPOSITOR_EXPORT LayerAnimator
   // with preemption strategies that discard previous animations.
   bool adding_animations_;
 
+  // Helper to output UMA performance metrics.
+  AnimationMetricsReporter* animation_metrics_reporter_;
+
   // Observers are notified when layer animations end, are scheduled or are
   // aborted.
   base::ObserverList<LayerAnimationObserver> observers_;