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

cc/scheduler/scheduler.cc

Index: cc/scheduler/scheduler.cc
diff --git a/cc/scheduler/scheduler.cc b/cc/scheduler/scheduler.cc
index ed8c0a2d3487a471180ced8a5809fc94a5f4fea8..904a0574515dac727b021f59386a721a0bb2f3c7 100644
--- a/cc/scheduler/scheduler.cc
+++ b/cc/scheduler/scheduler.cc
@@ -335,6 +335,9 @@ void Scheduler::SetupNextBeginFrameIfNeeded() {
   if (state_machine_.ShouldSetNeedsBeginFrames(
           frame_source_->NeedsBeginFrames())) {
     frame_source_->SetNeedsBeginFrames(state_machine_.BeginFrameNeeded());
+    if (!frame_source_->NeedsBeginFrames()) {
+      client_->SendBeginMainFrameNotExpectedSoon();
+    }
   }
 
   if (state_machine_.begin_impl_frame_state() ==