Hook up ui::Compositor to Display's BeginFrameSource

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 b5477f2e5353f9bc4386d408b2f1b195d70c8f58..554cf0169cc7a022d8b3e84392f2cd019c26de94 100644
--- a/cc/trees/single_thread_proxy.h
+++ b/cc/trees/single_thread_proxy.h
@@ -82,6 +82,7 @@ class CC_EXPORT SingleThreadProxy : public Proxy,
   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 DidSwapBuffersOnImplThread() override;
   void DidSwapBuffersCompleteOnImplThread() override;