WIP: Surface Synchronization System

cc/surfaces/surface_id_allocator.h

Index: cc/surfaces/surface_id_allocator.h
diff --git a/cc/surfaces/surface_id_allocator.h b/cc/surfaces/surface_id_allocator.h
index 8d2d79f025ec57e792c8e62ec7fad1bbcfd4529c..ab270a22b69be1eae930366c488bf4f287d27040 100644
--- a/cc/surfaces/surface_id_allocator.h
+++ b/cc/surfaces/surface_id_allocator.h
@@ -21,10 +21,15 @@ class CC_SURFACES_EXPORT SurfaceIdAllocator {
   SurfaceIdAllocator();
   ~SurfaceIdAllocator();
 
-  LocalFrameId GenerateId();
+  const LocalFrameId& GenerateId();
+
+  const LocalFrameId& current_local_frame_id() const {
+    return current_local_frame_id_;
+  }
 
  private:
   uint32_t next_id_;
+  LocalFrameId current_local_frame_id_;
 
   DISALLOW_COPY_AND_ASSIGN(SurfaceIdAllocator);
 };