Delete VideoFrame default constructor, and IsZeroSize method.

webrtc/modules/video_coding/codecs/i420/include/i420.h

 /*
  *  Copyright (c) 2012 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 113 matching lines @@
   //
   // Return value                : WEBRTC_VIDEO_CODEC_OK if OK.
   //                                  <0 - Error
   int Release() override;
 
  private:
   static const uint8_t* ExtractHeader(const uint8_t* buffer,
                                       uint16_t* width,
                                       uint16_t* height);
 
-  VideoFrame _decodedImage;
   int _width;
   int _height;
   bool _inited;
   DecodedImageCallback* _decodeCompleteCallback;
 };  // class I420Decoder
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_VIDEO_CODING_CODECS_I420_INCLUDE_I420_H_