Use microsecond timestamp in cricket::VideoFrame.

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 cb280b5e153beb20b69adb9565073d64681dce08..2913e8b429b9df3e021c4b892355d32cc91c7dd8 100644
--- a/webrtc/media/engine/webrtcvideoframe.h
+++ b/webrtc/media/engine/webrtcvideoframe.h
@@ -27,6 +27,11 @@ struct CapturedFrame;
 class WebRtcVideoFrame : public VideoFrame {
  public:
   WebRtcVideoFrame();
+  // TODO(nisse): Find a way to transition to using us units for the
+  // constructor and init methods. Maybe it's easiest to drop the
+  // timestamp argument, and require a separate method call for
+  // setting the timestamp?
+
   WebRtcVideoFrame(const rtc::scoped_refptr<webrtc::VideoFrameBuffer>& buffer,
                    int64_t time_stamp_ns,
                    webrtc::VideoRotation rotation);
@@ -49,6 +54,7 @@ class WebRtcVideoFrame : public VideoFrame {
 
   bool Init(const CapturedFrame* frame, int dw, int dh, bool apply_rotation);
 
+  void InitToEmptyBuffer(int w, int h);
   void InitToEmptyBuffer(int w, int h, int64_t time_stamp_ns);
 
   bool InitToBlack(int w, int h, int64_t time_stamp_ns);
@@ -69,10 +75,9 @@ class WebRtcVideoFrame : public VideoFrame {
   rtc::scoped_refptr<webrtc::VideoFrameBuffer> GetVideoFrameBuffer()
       const override;
 
-  int64_t GetTimeStamp() const override { return time_stamp_ns_; }
-  void SetTimeStamp(int64_t time_stamp_ns) override {
-    time_stamp_ns_ = time_stamp_ns;
-  }
+  /* System monotonic clock */
+  int64_t timestamp_us() const override { return timestamp_us_; }
+  void set_timestamp_us(int64_t time_us) { timestamp_us_ = time_us; };
 
   webrtc::VideoRotation GetVideoRotation() const override {
     return rotation_;
@@ -103,7 +108,6 @@ class WebRtcVideoFrame : public VideoFrame {
                      int dh,
                      uint8_t* sample,
                      size_t sample_size,
-                     int64_t time_stamp_ns,
                      webrtc::VideoRotation rotation,
                      bool apply_rotation);
 
@@ -113,7 +117,7 @@ class WebRtcVideoFrame : public VideoFrame {
 
   // An opaque reference counted handle that stores the pixel data.
   rtc::scoped_refptr<webrtc::VideoFrameBuffer> video_frame_buffer_;
-  int64_t time_stamp_ns_;
+  int64_t timestamp_us_;
   webrtc::VideoRotation rotation_;
 
   // This is mutable as the calculation is expensive but once calculated, it