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

content/renderer/scheduler/null_renderer_scheduler.h

Index: content/renderer/scheduler/null_renderer_scheduler.h
diff --git a/content/renderer/scheduler/null_renderer_scheduler.h b/content/renderer/scheduler/null_renderer_scheduler.h
index 5c5cf83e6f2026deee4219acf159959c4bcb63ed..b12034de927a8e4950b84a052cc6754f3aea0c2c 100644
--- a/content/renderer/scheduler/null_renderer_scheduler.h
+++ b/content/renderer/scheduler/null_renderer_scheduler.h
@@ -20,6 +20,7 @@ class NullRendererScheduler : public RendererScheduler {
   scoped_refptr<SingleThreadIdleTaskRunner> IdleTaskRunner() override;
 
   void WillBeginFrame(const cc::BeginFrameArgs& args) override;
+  void BeginFrameNoLongerRequired() override;
   void DidCommitFrameToCompositor() override;
   void DidReceiveInputEventOnCompositorThread(
       blink::WebInputEvent::Type type) override;