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 8bf87802f0c5daf5f6df040489100055a9b20896..b04080ae88d4bf393a343f64402d548e78bed41f 100644
--- a/content/renderer/gpu/render_widget_compositor.cc
+++ b/content/renderer/gpu/render_widget_compositor.cc
@@ -654,6 +654,10 @@ bool RenderWidgetCompositor::SendMessageToMicroBenchmark(
   return layer_tree_host_->SendMessageToMicroBenchmark(id, std::move(value));
 }
 
+cc::FrameSinkId RenderWidgetCompositor::getFrameSinkId() {
+  return frame_sink_id_;
+}
+
 void RenderWidgetCompositor::setRootLayer(const blink::WebLayer& layer) {
   layer_tree_host_->GetLayerTree()->SetRootLayer(
       static_cast<const cc_blink::WebLayerImpl*>(&layer)->layer());