Add a mojo channel for frame messages.

content/renderer/render_widget.cc

Index: content/renderer/render_widget.cc
diff --git a/content/renderer/render_widget.cc b/content/renderer/render_widget.cc
index dd984d51f973cfd4a1edb48a4b3539efa1540b06..2392b400fafcc0cbc86148cadac842b6d72ced34 100644
--- a/content/renderer/render_widget.cc
+++ b/content/renderer/render_widget.cc
@@ -839,6 +839,10 @@ void RenderWidget::SendInputEventAck(blink::WebInputEvent::Type type,
   Send(new InputHostMsg_HandleInputEvent_ACK(routing_id_, ack));
 }
 
+scoped_refptr<MainThreadEventQueue> RenderWidget::GetInputEventQueue() {
+  return input_event_queue_;
+}
+
 void RenderWidget::OnCursorVisibilityChange(bool is_visible) {
   if (GetWebWidget())
     GetWebWidget()->SetCursorVisibilityState(is_visible);