[animations] Adds metrics for jank on selected layer animations

ui/compositor/compositor.h

Index: ui/compositor/compositor.h
diff --git a/ui/compositor/compositor.h b/ui/compositor/compositor.h
index 25bad57a8c55954d1cce700dec32395f9683a1ef..02ed316ccd1665068edf35546eceaa15b2b32abc 100644
--- a/ui/compositor/compositor.h
+++ b/ui/compositor/compositor.h
@@ -380,6 +380,7 @@ class COMPOSITOR_EXPORT Compositor
   }
 
   const cc::FrameSinkId& frame_sink_id() const { return frame_sink_id_; }
+  int committed_frame_number() const { return committed_frame_number_; }
 
  private:
   friend class base::RefCounted<Compositor>;
@@ -403,6 +404,8 @@ class COMPOSITOR_EXPORT Compositor
   base::ObserverList<CompositorAnimationObserver> animation_observer_list_;
 
   gfx::AcceleratedWidget widget_;
+  // A sequence number of a current compositor frame for use with metrics.
+  int committed_frame_number_;
   // A map from child id to parent id.
   std::unordered_set<cc::FrameSinkId, cc::FrameSinkIdHash> child_frame_sinks_;
   bool widget_valid_;