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

content/test/fake_renderer_scheduler.h

Index: content/test/fake_renderer_scheduler.h
diff --git a/content/test/fake_renderer_scheduler.h b/content/test/fake_renderer_scheduler.h
index 822231429e1842cf927ca75b229f95ca076fd8b4..dc3e16ed5a5c5755b851a8a6789723d57cbc83d1 100644
--- a/content/test/fake_renderer_scheduler.h
+++ b/content/test/fake_renderer_scheduler.h
@@ -20,6 +20,7 @@ class FakeRendererScheduler : public RendererScheduler {
   scoped_refptr<base::SingleThreadTaskRunner> LoadingTaskRunner() override;
   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;