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 66e00758a517fb4ab76031b544ee75577f9ff107..5095715f842c1bd50b89fd41a30c0bc4563fa6ff 100644
--- a/cc/trees/single_thread_proxy.h
+++ b/cc/trees/single_thread_proxy.h
@@ -81,6 +81,7 @@ 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;