Implement support for 2-pattern cadence.

media/filters/video_renderer_algorithm.h

Index: media/filters/video_renderer_algorithm.h
diff --git a/media/filters/video_renderer_algorithm.h b/media/filters/video_renderer_algorithm.h
index e7303839c648e2aca1140b6964d2e1976e51a7c4..ee4d4c4e6f2e616d22e2ae92502992ba0e9fa304 100644
--- a/media/filters/video_renderer_algorithm.h
+++ b/media/filters/video_renderer_algorithm.h
@@ -189,7 +189,8 @@ class MEDIA_EXPORT VideoRendererAlgorithm {
   bool UpdateFrameStatistics();
 
   // Updates the ideal render count for all frames in |frame_queue_| based on
-  // the cadence returned by |cadence_estimator_|.
+  // the cadence returned by |cadence_estimator_|.  Cadence is assigned based
+  // on |frame_counter_|.
   void UpdateCadenceForFrames();
 
   // If |cadence_estimator_| has detected a valid cadence, attempts to find the
@@ -292,6 +293,13 @@ class MEDIA_EXPORT VideoRendererAlgorithm {
   // until the first frame has reached its presentation time.
   bool first_frame_;
 
+  // The frame number of the last rendered frame; incremented for every frame
+  // rendered and every frame dropped or expired since the last rendered frame.
+  //
+  // Given to |cadence_estimator_| when assigning cadence values to the
+  // ReadyFrameQueue.  Cleared when a new cadence is detected.
+  uint64_t cadence_frame_counter_;
+
   DISALLOW_COPY_AND_ASSIGN(VideoRendererAlgorithm);
 };