Pass a TimeTicks along video capture pipeline to represent capture time

content/public/renderer/media_stream_video_sink.h

Index: content/public/renderer/media_stream_video_sink.h
diff --git a/content/public/renderer/media_stream_video_sink.h b/content/public/renderer/media_stream_video_sink.h
index 663f3a86f072d4ca2907877ae60ef9949dda47e6..7aa2a5e8850cf2fa5034345c9b91dbc2de40eb0d 100644
--- a/content/public/renderer/media_stream_video_sink.h
+++ b/content/public/renderer/media_stream_video_sink.h
@@ -8,6 +8,7 @@
 #include "base/callback.h"
 #include "base/compiler_specific.h"
 #include "base/memory/ref_counted.h"
+#include "base/time/time.h"
 #include "content/common/content_export.h"
 #include "content/public/renderer/media_stream_sink.h"
 
@@ -22,10 +23,22 @@ class WebMediaStreamTrack;
 
 namespace content {
 
+// This callback is used to deliver video frames.
+// |estimated_capture_time| - An optional field to provide the capture time of
+// the delivered video frame. This field usually means the local time when the
+// video frame was generated. It is possible for this value to be null if this
+// timing information cannot be determined. There is no gurantee that this
+// value is accurate. For example video frames from a remote source can only
+// provide this timing information as an estimate.
+// |video_frame->timestamp()| gives the presentation timestamp of the video
+// frame relative to the first frame generated by the corresponding source.
+// Because a source can start generating frames before a subscriber is added,
+// the first video frame delivered may not have timestamp equal to 0.
 typedef base::Callback<
-  void(const scoped_refptr<media::VideoFrame>&,
-       const media::VideoCaptureFormat&)>
-    VideoSinkDeliverFrameCB;
+  void(const scoped_refptr<media::VideoFrame>& video_frame,
+       const media::VideoCaptureFormat& format,
+       const base::TimeTicks& estimated_capture_time)>
+    VideoCaptureDeliverFrameCB;
 
 // MediaStreamVideoSink is an interface used for receiving video frames from a
 // Video Stream Track or a Video Source.
@@ -44,7 +57,7 @@ class CONTENT_EXPORT MediaStreamVideoSink : public MediaStreamSink {
   // callback immediately because it may happen on another thread.
   // The added callback will be reset on the render thread.
   static void AddToVideoTrack(MediaStreamVideoSink* sink,
-                              const VideoSinkDeliverFrameCB& callback,
+                              const VideoCaptureDeliverFrameCB& callback,
                               const blink::WebMediaStreamTrack& track);
   static void RemoveFromVideoTrack(MediaStreamVideoSink* sink,
                                    const blink::WebMediaStreamTrack& track);