Expose codec implementation names in stats.

webrtc/modules/video_coding/codecs/h264/h264_video_toolbox_encoder.cc

 /*
  *  Copyright (c) 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.
  *
  */
@@ skipping 416 matching lines @@
 }
 
 void H264VideoToolboxEncoder::DestroyCompressionSession() {
   if (compression_session_) {
     VTCompressionSessionInvalidate(compression_session_);
     CFRelease(compression_session_);
     compression_session_ = nullptr;
   }
 }
 
+const char* H264VideoToolboxEncoder::ImplementationName() const {
+  return "VideoToolbox";
+}
+
 }  // namespace webrtc
 
 #endif  // defined(WEBRTC_VIDEO_TOOLBOX_SUPPORTED)