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 15 matching lines @@
         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
-    // tolerance on Y values.
-    black_frame_ = CheckFrameColorYuv(6, 48, 128, 128, 128, 128, &frame);
+    // tolerance on Y values. Some unit tests produce Y values close
+    // to 16 rather than close to zero, for supposedly black frames.
+    // Largest value observed is 34, e.g., running
+    // P2PTestConductor.LocalP2PTest16To9 (peerconnection_unittests).
+    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_