Revert of Remove default begin frame sources from the renderer

cc/trees/proxy_impl.h

Index: cc/trees/proxy_impl.h
diff --git a/cc/trees/proxy_impl.h b/cc/trees/proxy_impl.h
index 35ee0ccac55e42ea1f02059f788db08d4453ba00..13bc65f9cec628bc2f4c3435a02c69ce83a6a479 100644
--- a/cc/trees/proxy_impl.h
+++ b/cc/trees/proxy_impl.h
@@ -66,6 +66,8 @@
 
   // LayerTreeHostImplClient implementation
   void DidLoseOutputSurfaceOnImplThread() override;
+  void CommitVSyncParameters(base::TimeTicks timebase,
+                             base::TimeDelta interval) override;
   void SetBeginFrameSource(BeginFrameSource* source) override;
   void SetEstimatedParentDrawTime(base::TimeDelta draw_time) override;
   void DidSwapBuffersCompleteOnImplThread() override;
@@ -136,6 +138,8 @@
   DelayedUniqueNotifier smoothness_priority_expiration_notifier_;
 
   std::unique_ptr<BeginFrameSource> external_begin_frame_source_;
+  std::unique_ptr<BeginFrameSource> unthrottled_begin_frame_source_;
+  std::unique_ptr<SyntheticBeginFrameSource> synthetic_begin_frame_source_;
 
   RenderingStatsInstrumentation* rendering_stats_instrumentation_;