Make OffscreenCanvas animation in sync with its placeholder canvas's parent frame rate

content/renderer/gpu/render_widget_compositor.cc

Index: content/renderer/gpu/render_widget_compositor.cc
diff --git a/content/renderer/gpu/render_widget_compositor.cc b/content/renderer/gpu/render_widget_compositor.cc
index b9cdc15aa7d1c0f90bcf7d33b0253d186ddf6da8..78868250a1c8418e0d6d6b29c4c20ae682460b93 100644
--- a/content/renderer/gpu/render_widget_compositor.cc
+++ b/content/renderer/gpu/render_widget_compositor.cc
@@ -1118,6 +1118,10 @@ void RenderWidgetCompositor::SetFrameSinkId(
   layer_tree_host_->SetFrameSinkId(frame_sink_id);
 }
 
+cc::FrameSinkId RenderWidgetCompositor::getFrameSinkId() {
+  return frame_sink_id_;
+}
+
 void RenderWidgetCompositor::OnHandleCompositorProto(
     const std::vector<uint8_t>& proto) {
   DCHECK(remote_proto_channel_receiver_);