Making OutputSurface a begin frame source and vsync source.

cc/output/output_surface.h

Index: cc/output/output_surface.h
diff --git a/cc/output/output_surface.h b/cc/output/output_surface.h
index d3eca54fa83d98023e0c71e623785a5fd8422d8c..a723645a896159ca5dd40f3a5e0dccc69743dddb 100644
--- a/cc/output/output_surface.h
+++ b/cc/output/output_surface.h
@@ -16,6 +16,8 @@
 #include "cc/output/context_provider.h"
 #include "cc/output/overlay_candidate_validator.h"
 #include "cc/output/software_output_device.h"
+#include "cc/scheduler/frame_source.h"
+#include "ui/compositor/compositor_vsync_manager.h"
 
 namespace base { class SingleThreadTaskRunner; }
 
@@ -41,7 +43,7 @@ class OutputSurfaceClient;
 //      From here on, it will only be used on the compositor thread.
 //   3. If the 3D context is lost, then the compositor will delete the output
 //      surface (on the compositor thread) and go back to step 1.
-class CC_EXPORT OutputSurface {
+class CC_EXPORT OutputSurface : public BeginFrameSource {
  public:
   enum {
     DEFAULT_MAX_FRAMES_PENDING = 2
@@ -121,11 +123,6 @@ class CC_EXPORT OutputSurface {
   // processing should be stopped, or lowered in priority.
   virtual void UpdateSmoothnessTakesPriority(bool prefer_smoothness) {}
 
-  // Requests a BeginFrame notification from the output surface. The
-  // notification will be delivered by calling
-  // OutputSurfaceClient::BeginFrame until the callback is disabled.
-  virtual void SetNeedsBeginFrame(bool enable) {}
-
   bool HasClient() { return !!client_; }
 
   // Returns an estimate of the current GPU latency. When only a software
@@ -137,8 +134,22 @@ class CC_EXPORT OutputSurface {
     return overlay_candidate_validator_.get();
   }
 
+  void AddVSyncObserver(ui::CompositorVSyncManager::Observer* obs) {
+    vsync_observer_ = obs;
+  };
+
+  // BeginFrameSource
+  virtual void SetNeedsBeginFrames(bool needs_begin_frames) OVERRIDE;
+  virtual bool NeedsBeginFrames() const OVERRIDE;
+  virtual void DidFinishFrame(size_t remaining_frames) OVERRIDE {}
+  virtual void AsValueInto(base::debug::TracedValue* dict) const OVERRIDE;
+
  protected:
+  bool needs_begin_frames_ = false;
+
   OutputSurfaceClient* client_;
+  ui::CompositorVSyncManager::Observer* vsync_observer_;
+  BeginFrameObserver* begin_frame_observer_;
 
   // Synchronously initialize context3d and enter hardware mode.
   // This can only supported in threaded compositing mode.