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

cc/scheduler/scheduler.h

Index: cc/scheduler/scheduler.h
diff --git a/cc/scheduler/scheduler.h b/cc/scheduler/scheduler.h
index e06a133dd8abe6709b19569a7db9d32fee883367..bdcb886617010bd91dade2374856d8434f435449 100644
--- a/cc/scheduler/scheduler.h
+++ b/cc/scheduler/scheduler.h
@@ -49,6 +49,7 @@ class SchedulerClient {
   virtual base::TimeDelta CommitToActivateDurationEstimate() = 0;
   virtual void DidBeginImplFrameDeadline() = 0;
   virtual void SendBeginFramesToChildren(const BeginFrameArgs& args) = 0;
+  virtual void SendBeginMainFrameNoLongerRequired() = 0;
 
  protected:
   virtual ~SchedulerClient() {}