cc: Add SetChildrenNeedBeginFrames() & SendBeginFramesToChildren()

cc/trees/layer_tree_host_client.h

Index: cc/trees/layer_tree_host_client.h
diff --git a/cc/trees/layer_tree_host_client.h b/cc/trees/layer_tree_host_client.h
index dca389da82d60e58915848eafb7151224549aaec..5b02964e89f019c9f45798e7297c8b6380171dcf 100644
--- a/cc/trees/layer_tree_host_client.h
+++ b/cc/trees/layer_tree_host_client.h
@@ -45,6 +45,10 @@ class LayerTreeHostClient {
   virtual void DidCommitAndDrawFrame() = 0;
   virtual void DidCompleteSwapBuffers() = 0;
 
+  // TODO(simonhong): Makes this to pure virtual function when client
+  // implementation is ready.
+  virtual void SendBeginFramesToChildren(const BeginFrameArgs& args) {}
+
   // Requests that the client insert a rate limiting token in the shared main
   // thread context's command stream that will block if the context gets too far
   // ahead of the compositor's command stream. Only needed if the tree contains