Update bitrate adjustment with true buffer used size.

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 713 matching lines @@
 
   h264_bitstream_parser_.ParseBitstream(buffer->data(), buffer->size());
   h264_bitstream_parser_.GetLastSliceQp(&frame.qp_);
 
   EncodedImageCallback::Result res =
       callback_->OnEncodedImage(frame, &codec_specific_info, header.get());
   if (res.error != EncodedImageCallback::Result::OK) {
     LOG(LS_ERROR) << "Encode callback failed: " << res.error;
     return;
   }
-  bitrate_adjuster_.Update(frame._size);
+  bitrate_adjuster_.Update(frame._length);
 }
 
 VideoEncoder::ScalingSettings H264VideoToolboxEncoder::GetScalingSettings()
     const {
   return VideoEncoder::ScalingSettings(true, internal::kLowH264QpThreshold,
                                        internal::kHighH264QpThreshold);
 }
 }  // namespace webrtc