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

cc/trees/layer_tree_host.h

Index: cc/trees/layer_tree_host.h
diff --git a/cc/trees/layer_tree_host.h b/cc/trees/layer_tree_host.h
index 7db722f61f35a91aa2d19a720bfb4721774fd6c8..f33a06b75610c5495c437c385077698c702f4647 100644
--- a/cc/trees/layer_tree_host.h
+++ b/cc/trees/layer_tree_host.h
@@ -115,6 +115,7 @@ class CC_EXPORT LayerTreeHost {
   }
   void DidBeginMainFrame();
   void BeginMainFrame(const BeginFrameArgs& args);
+  void BeginMainFrameNoLongerRequired();
   void AnimateLayers(base::TimeTicks monotonic_frame_begin_time);
   void DidStopFlinging();
   void Layout();