Hook up ui::Compositor to Display's BeginFrameSource

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 a335d8abe1ac4e75ce7e017221ad6857234c92c6..557705fb9cf0272139f29bd93c4ff906c657c08f 100644
--- a/cc/trees/proxy_impl.h
+++ b/cc/trees/proxy_impl.h
@@ -78,6 +78,7 @@ class CC_EXPORT ProxyImpl : public NON_EXPORTED_BASE(LayerTreeHostImplClient),
   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;