[cc] Don't send missed BeginFrames with past deadline.

cc/scheduler/begin_frame_source.h

Index: cc/scheduler/begin_frame_source.h
diff --git a/cc/scheduler/begin_frame_source.h b/cc/scheduler/begin_frame_source.h
index 1e1938ba40f3967d652d3b3625950d6fb11d4a73..4b5519f80a1387cc959af89ae3d4d9eb90d580ba 100644
--- a/cc/scheduler/begin_frame_source.h
+++ b/cc/scheduler/begin_frame_source.h
@@ -311,6 +311,9 @@ class CC_EXPORT ExternalBeginFrameSource : public BeginFrameSource {
   void MaybeFinishFrame();
   void FinishFrame();
 
+  // Virtual for testing.
+  virtual base::TimeTicks Now() const;
+
   BeginFrameArgs missed_begin_frame_args_;
   std::unordered_set<BeginFrameObserver*> observers_;
   ExternalBeginFrameSourceClient* client_;