Revert of Delete VideoFrame default constructor, and IsZeroSize method.

webrtc/modules/video_coding/codecs/vp8/simulcast_encoder_adapter.cc

 /*
  *  Copyright (c) 2014 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 279 matching lines @@
     // matches the destination or the input image is empty (e.g.
     // a keyframe request for encoders with internal camera
     // sources) or the source image has a native handle, pass the image on
     // directly. Otherwise, we'll scale it to match what the encoder expects
     // (below).
     // For texture frames, the underlying encoder is expected to be able to
     // correctly sample/scale the source texture.
     // TODO(perkj): ensure that works going forward, and figure out how this
     // affects webrtc:5683.
     if ((dst_width == src_width && dst_height == src_height) ||
+        input_image.IsZeroSize() ||
         input_image.video_frame_buffer()->native_handle()) {
       int ret = streaminfos_[stream_idx].encoder->Encode(
           input_image, codec_specific_info, &stream_frame_types);
       if (ret != WEBRTC_VIDEO_CODEC_OK) {
         return ret;
       }
     } else {
       // Aligning stride values based on width.
       rtc::scoped_refptr<I420Buffer> dst_buffer =
           I420Buffer::Create(dst_width, dst_height, dst_width,
@@ skipping 156 matching lines @@
   if (NumberOfStreams(codec_) != 1)
     return VideoEncoder::ScalingSettings(false);
   return streaminfos_[0].encoder->GetScalingSettings();
 }
 
 const char* SimulcastEncoderAdapter::ImplementationName() const {
   return implementation_name_.c_str();
 }
 
 }  // namespace webrtc