New static method I420Buffer::SetToBlack.

webrtc/media/base/fakevideorenderer.h

 /*
  *  Copyright (c) 2011 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 14 matching lines @@
       : errors_(0),
         width_(0),
         height_(0),
         rotation_(webrtc::kVideoRotation_0),
         timestamp_(0),
         num_rendered_frames_(0),
         black_frame_(false) {}
 
   virtual void OnFrame(const VideoFrame& frame) {
     rtc::CritScope cs(&crit_);
     // TODO(zhurunz) Check with VP8 team to see if we can remove this

[perkj_webrtc, 2016/06/02 13:20:04]

remove this TODO if this works.

[nisse-webrtc, 2016/06/03 14:22:50]

I logged the largest Y value seen  supposedly black frames, and the largest
value seen when run rtc_media_unittests and peerconnection_unittests were 34.

So using 48 as the upper bound seems quite reasonable.

[pbos-webrtc, 2016/06/03 14:46:02]

That means that we cannot remove it right? Update the comment to say why we
permit non-exact Y?

[nisse-webrtc, 2016/06/08 09:25:28]

Done.

     // tolerance on Y values.
-    black_frame_ = CheckFrameColorYuv(6, 48, 128, 128, 128, 128, &frame);
+    black_frame_ = CheckFrameColorYuv(0, 48, 128, 128, 128, 128, &frame);
     // Treat unexpected frame size as error.
     ++num_rendered_frames_;
     width_ = frame.width();
     height_ = frame.height();
     rotation_ = frame.rotation();
     timestamp_ = frame.GetTimeStamp();
     SignalRenderFrame(&frame);
   }
 
   int errors() const { return errors_; }
@@ skipping 84 matching lines @@
   webrtc::VideoRotation rotation_;
   int64_t timestamp_;
   int num_rendered_frames_;
   bool black_frame_;
   rtc::CriticalSection crit_;
 };
 
 }  // namespace cricket
 
 #endif  // WEBRTC_MEDIA_BASE_FAKEVIDEORENDERER_H_