[cc]: Add a BeginMainFrameNotExpectedSoon signal and route it to the RendererScheduler.

mojo/services/html_viewer/weblayertreeview_impl.cc

Index: mojo/services/html_viewer/weblayertreeview_impl.cc
diff --git a/mojo/services/html_viewer/weblayertreeview_impl.cc b/mojo/services/html_viewer/weblayertreeview_impl.cc
index a1d4da82c260e571621dfaa74ac8a2ec93311983..e806d10dcd40b8aa4adce2e49b4c6f4884561c06 100644
--- a/mojo/services/html_viewer/weblayertreeview_impl.cc
+++ b/mojo/services/html_viewer/weblayertreeview_impl.cc
@@ -65,6 +65,9 @@ void WebLayerTreeViewImpl::WillBeginMainFrame() {
 void WebLayerTreeViewImpl::DidBeginMainFrame() {
 }
 
+void WebLayerTreeViewImpl::BeginMainFrameNotExpectedSoon() {
+}
+
 void WebLayerTreeViewImpl::BeginMainFrame(const cc::BeginFrameArgs& args) {
   VLOG(2) << "WebLayerTreeViewImpl::BeginMainFrame";
   double frame_time_sec = (args.frame_time - base::TimeTicks()).InSecondsF();