Delete VideoFrame default constructor, and IsZeroSize method.

webrtc/modules/video_coding/codecs/h264/h264_encoder_impl.cc

Index: webrtc/modules/video_coding/codecs/h264/h264_encoder_impl.cc
diff --git a/webrtc/modules/video_coding/codecs/h264/h264_encoder_impl.cc b/webrtc/modules/video_coding/codecs/h264/h264_encoder_impl.cc
index d7df12209d1897718c456f3b845011cb1f82a417..7e1420000d99523f7ce16a43ab667d401544ef8e 100644
--- a/webrtc/modules/video_coding/codecs/h264/h264_encoder_impl.cc
+++ b/webrtc/modules/video_coding/codecs/h264/h264_encoder_impl.cc
@@ -294,10 +294,6 @@ int32_t H264EncoderImpl::Encode(const VideoFrame& input_frame,
     ReportError();
     return WEBRTC_VIDEO_CODEC_UNINITIALIZED;
   }
-  if (input_frame.IsZeroSize()) {
-    ReportError();
-    return WEBRTC_VIDEO_CODEC_ERR_PARAMETER;
-  }
   if (!encoded_image_callback_) {
     LOG(LS_WARNING) << "InitEncode() has been called, but a callback function "
                     << "has not been set with RegisterEncodeCompleteCallback()";