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..a558aba93fd73d06209932e6e6b8bac3d774e1bb 100644
--- a/content/renderer/gpu/render_widget_compositor.cc
+++ b/content/renderer/gpu/render_widget_compositor.cc
@@ -668,6 +668,10 @@ 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());