Revert of Remove default begin frame sources from the renderer

cc/trees/single_thread_proxy.h

Index: cc/trees/single_thread_proxy.h
diff --git a/cc/trees/single_thread_proxy.h b/cc/trees/single_thread_proxy.h
index 4fc3bea10be08fce9492c3132404092a34715e5a..95349246741c59e93dfe8d5d2b423cd5971da4ac 100644
--- a/cc/trees/single_thread_proxy.h
+++ b/cc/trees/single_thread_proxy.h
@@ -76,6 +76,8 @@
 
   // 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;
@@ -135,6 +137,8 @@
 
   // Accessed from both threads.
   std::unique_ptr<BeginFrameSource> external_begin_frame_source_;
+  std::unique_ptr<BeginFrameSource> unthrottled_begin_frame_source_;
+  std::unique_ptr<SyntheticBeginFrameSource> synthetic_begin_frame_source_;
   std::unique_ptr<Scheduler> scheduler_on_impl_thread_;
 
   std::unique_ptr<BlockingTaskRunner::CapturePostTasks>