Add cricket::VideoFrame::frame_id() and set it to RTP timestamp.

webrtc/media/engine/webrtcvideoframe.h

Index: webrtc/media/engine/webrtcvideoframe.h
diff --git a/webrtc/media/engine/webrtcvideoframe.h b/webrtc/media/engine/webrtcvideoframe.h
index 487e32ef9af23630f749f65dca93558d80555eef..da204533db631ecbf22ba217b74ed372961bedb9 100644
--- a/webrtc/media/engine/webrtcvideoframe.h
+++ b/webrtc/media/engine/webrtcvideoframe.h
@@ -31,11 +31,12 @@ class WebRtcVideoFrame : public VideoFrame {
   // Preferred construction, with microsecond timestamp.
   WebRtcVideoFrame(const rtc::scoped_refptr<webrtc::VideoFrameBuffer>& buffer,
                    webrtc::VideoRotation rotation,
-                   int64_t timestamp_us);
+                   int64_t timestamp_us,
+                   uint32_t frame_id);
 
   // TODO(nisse): Deprecate/delete.
   WebRtcVideoFrame(const rtc::scoped_refptr<webrtc::VideoFrameBuffer>& buffer,
-                   int64_t time_stamp_ns,
+                   int64_t timestamp_ns,
                    webrtc::VideoRotation rotation);
 
   ~WebRtcVideoFrame();
@@ -51,7 +52,7 @@ class WebRtcVideoFrame : public VideoFrame {
             int dh,
             uint8_t* sample,
             size_t sample_size,
-            int64_t time_stamp_ns,
+            int64_t timestamp_ns,
             webrtc::VideoRotation rotation);
 
   // The timestamp of the captured frame is expected to use the same
@@ -69,11 +70,12 @@ class WebRtcVideoFrame : public VideoFrame {
   const rtc::scoped_refptr<webrtc::VideoFrameBuffer>& video_frame_buffer()
       const override;
 
-  /* System monotonic clock */
-  int64_t timestamp_us() const override { return timestamp_us_; }
-  void set_timestamp_us(int64_t time_us) override { timestamp_us_ = time_us; };
+  uint32_t frame_id() const override;
 
-  webrtc::VideoRotation rotation() const override { return rotation_; }
+  int64_t timestamp_us() const override;
+  void set_timestamp_us(int64_t time_us) override;
+
+  webrtc::VideoRotation rotation() const override;
 
   VideoFrame* Copy() const override;
 
@@ -111,6 +113,7 @@ class WebRtcVideoFrame : public VideoFrame {
   // An opaque reference counted handle that stores the pixel data.
   rtc::scoped_refptr<webrtc::VideoFrameBuffer> video_frame_buffer_;
   int64_t timestamp_us_;
+  uint32_t frame_id_;
   webrtc::VideoRotation rotation_;
 
   // This is mutable as the calculation is expensive but once calculated, it