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

cc/test/scheduler_test_common.h

Index: cc/test/scheduler_test_common.h
diff --git a/cc/test/scheduler_test_common.h b/cc/test/scheduler_test_common.h
index 49612059d0632eeb7395ffe0f64a851acde01ac8..631ae72ea2ce616df7cb27f5e96b0559ffe97811 100644
--- a/cc/test/scheduler_test_common.h
+++ b/cc/test/scheduler_test_common.h
@@ -144,6 +144,8 @@ class TestScheduler : public Scheduler {
     return begin_frame_source_ && observing_begin_frame_source_;
   }
 
+  bool BeginFrameNeeded() const { return state_machine_.BeginFrameNeeded(); }
+
   int current_frame_number() const {
     return state_machine_.current_frame_number();
   }