Preliminary change for new rtc rendering algorithm

media/base/video_frame_metadata.h

Index: media/base/video_frame_metadata.h
diff --git a/media/base/video_frame_metadata.h b/media/base/video_frame_metadata.h
index bd330f0ed3bfa598ded89b9cc9915a58e7405ca0..48fe509719fc9e3f724086903af85a7845b709cf 100644
--- a/media/base/video_frame_metadata.h
+++ b/media/base/video_frame_metadata.h
@@ -50,6 +50,15 @@ class MEDIA_EXPORT VideoFrameMetadata {
     // key.
     FRAME_RATE,
 
+    // This field represents the local time at which either: 1) the frame was
+    // generated, if it was done so locally; or 2) the targeted play-out time
+    // of the frame, if it was generated from a remote source. This value is NOT
+    // a high-resolution timestamp, and so it should not be used as a
+    // presentation time; but, instead, it should be used for buffering playback
+    // and for A/V synchronization purposes.
+    // Use Get/SetTimeTicks() for this key.
+    REFERENCE_TIME,
+
     // A feedback signal that indicates the fraction of the tolerable maximum
     // amount of resources that were utilized to process this frame.  A producer
     // can check this value after-the-fact, usually via a VideoFrame destruction