Add BeginFrameObserverProxy

ui/compositor/compositor.h

Index: ui/compositor/compositor.h
diff --git a/ui/compositor/compositor.h b/ui/compositor/compositor.h
index 47d4cd0d7e30866f980299191cd5994d386673b9..561fee610e6005b0e1a614009e539152d2e5b970 100644
--- a/ui/compositor/compositor.h
+++ b/ui/compositor/compositor.h
@@ -13,6 +13,7 @@
 #include "base/observer_list.h"
 #include "base/single_thread_task_runner.h"
 #include "base/time/time.h"
+#include "cc/output/begin_frame_args.h"
 #include "cc/surfaces/surface_sequence.h"
 #include "cc/trees/layer_tree_host_client.h"
 #include "cc/trees/layer_tree_host_single_thread_client.h"
@@ -131,6 +132,14 @@ class COMPOSITOR_EXPORT CompositorLock
   DISALLOW_COPY_AND_ASSIGN(CompositorLock);
 };
 
+// This class observes BeginFrame notification from LayerTreeHost.
+class COMPOSITOR_EXPORT CompositorBeginFrameObserver {
+ public:
+  virtual ~CompositorBeginFrameObserver() {}
+
+  virtual void OnSendBeginFrame(const cc::BeginFrameArgs& args) = 0;
+};
+
 // Compositor object to take care of GPU painting.
 // A Browser compositor object is responsible for generating the final
 // displayable form of pixels comprising a single widget's contents. It draws an
@@ -226,6 +235,11 @@ class COMPOSITOR_EXPORT Compositor
   void RemoveAnimationObserver(CompositorAnimationObserver* observer);
   bool HasAnimationObserver(const CompositorAnimationObserver* observer) const;
 
+  void AddBeginFrameObserver(
+      CompositorBeginFrameObserver* observer,
+      const cc::BeginFrameArgs& last_begin_frame_args_sent_to_observer);
+  void RemoveBeginFrameObserver(CompositorBeginFrameObserver* observer);
+
   // Creates a compositor lock. Returns NULL if it is not possible to lock at
   // this time (i.e. we're waiting to complete a previous unlock).
   scoped_refptr<CompositorLock> GetCompositorLock();
@@ -264,6 +278,7 @@ class COMPOSITOR_EXPORT Compositor
   void DidCommitAndDrawFrame() override;
   void DidCompleteSwapBuffers() override;
   void DidCompletePageScaleAnimation() override {}
+  void SendBeginFramesToChildren(const cc::BeginFrameArgs& args) override;
 
   // cc::LayerTreeHostSingleThreadClient implementation.
   void DidPostSwapBuffers() override;
@@ -283,6 +298,11 @@ class COMPOSITOR_EXPORT Compositor
     return surface_id_allocator_.get();
   }
 
+  // Exposed for testing
+  cc::BeginFrameArgs MissedBeginFrameArgsForTesting() {
+    return missed_begin_frame_args_;
+  }
+
  private:
   friend class base::RefCounted<Compositor>;
   friend class CompositorLock;
@@ -302,6 +322,7 @@ class COMPOSITOR_EXPORT Compositor
 
   ObserverList<CompositorObserver, true> observer_list_;
   ObserverList<CompositorAnimationObserver> animation_observer_list_;
+  ObserverList<CompositorBeginFrameObserver> begin_frame_observer_list_;
 
   gfx::AcceleratedWidget widget_;
   scoped_ptr<cc::SurfaceIdAllocator> surface_id_allocator_;
@@ -325,6 +346,9 @@ class COMPOSITOR_EXPORT Compositor
 
   LayerAnimatorCollection layer_animator_collection_;
 
+  // Used to send to any new CompositorBeginFrameObserver immediately.
+  cc::BeginFrameArgs missed_begin_frame_args_;
+
   base::WeakPtrFactory<Compositor> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(Compositor);