Revert of Delete VideoFrame default constructor, and IsZeroSize method.

webrtc/sdk/objc/Framework/Classes/h264_video_toolbox_encoder.mm

 /*
  *  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 362 matching lines @@
   return ResetCompressionSession();
 }
 
 int H264VideoToolboxEncoder::Encode(
     const VideoFrame& frame,
     const CodecSpecificInfo* codec_specific_info,
     const std::vector<FrameType>* frame_types) {
   // |input_frame| size should always match codec settings.
   RTC_DCHECK_EQ(frame.width(), width_);
   RTC_DCHECK_EQ(frame.height(), height_);
+  RTC_DCHECK(!frame.IsZeroSize());
   if (!callback_ || !compression_session_) {
     return WEBRTC_VIDEO_CODEC_UNINITIALIZED;
   }
 #if defined(WEBRTC_IOS)
   if (!RTCIsUIApplicationActive()) {
     // Ignore all encode requests when app isn't active. In this state, the
     // hardware encoder has been invalidated by the OS.
     return WEBRTC_VIDEO_CODEC_OK;
   }
 #endif
@@ skipping 336 matching lines @@
   }
   bitrate_adjuster_.Update(frame._size);
 }
 
 VideoEncoder::ScalingSettings H264VideoToolboxEncoder::GetScalingSettings()
     const {
   return VideoEncoder::ScalingSettings(true, internal::kLowH264QpThreshold,
                                        internal::kHighH264QpThreshold);
 }
 }  // namespace webrtc