[cc] Calculate the correct latest_confirmed_sequence_number in cc::Scheduler.

cc/scheduler/scheduler.h

Index: cc/scheduler/scheduler.h
diff --git a/cc/scheduler/scheduler.h b/cc/scheduler/scheduler.h
index 5fd4c92e8d953cdd316bb5d8296963e536618973..81a0a345c418af31f19c0630369513c58e26f3e0 100644
--- a/cc/scheduler/scheduler.h
+++ b/cc/scheduler/scheduler.h
@@ -206,6 +206,8 @@ class CC_EXPORT Scheduler : public BeginFrameObserverBase {
   void BeginImplFrameSynchronous(const BeginFrameArgs& args);
   void BeginImplFrame(const BeginFrameArgs& args);
   void FinishImplFrame();
+  enum BeginFrameResult { kBeginFrameSkipped, kBeginFrameFinished };
+  void SendBeginFrameAck(const BeginFrameArgs& args, BeginFrameResult result);
   void OnBeginImplFrameDeadline();
   void PollToAdvanceCommitState();