Reland of Injectable Obj-C video codecs

webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCVideoFrame.mm

 /*
  *  Copyright 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #import "webrtc/sdk/objc/Framework/Headers/WebRTC/RTCVideoFrame.h"
 #import "webrtc/sdk/objc/Framework/Headers/WebRTC/RTCVideoFrameBuffer.h"
 
 @implementation RTCVideoFrame {
   RTCVideoRotation _rotation;
   int64_t _timeStampNs;
 }
 
 @synthesize buffer = _buffer;
+@synthesize timeStamp;
 
 - (int)width {
   return _buffer.width;
 }
 
 - (int)height {
   return _buffer.height;
 }
 
 - (RTCVideoRotation)rotation {
@@ skipping 99 matching lines @@
   if (self = [super init]) {
     _buffer = buffer;
     _rotation = rotation;
     _timeStampNs = timeStampNs;
   }
 
   return self;
 }
 
 @end