Revert of Delete VideoFrame default constructor, and IsZeroSize method.

webrtc/common_video/video_frame.cc

Index: webrtc/common_video/video_frame.cc
diff --git a/webrtc/common_video/video_frame.cc b/webrtc/common_video/video_frame.cc
index d9c5c2f783cf6dcf7c0014112541017e5b04fb54..ab1a6bef408fdddce69fca01e510942fa645ca0d 100644
--- a/webrtc/common_video/video_frame.cc
+++ b/webrtc/common_video/video_frame.cc
@@ -22,6 +22,13 @@
 // FFmpeg's decoder, used by H264DecoderImpl, requires up to 8 bytes padding due
 // to optimized bitstream readers. See avcodec_decode_video2.
 const size_t EncodedImage::kBufferPaddingBytesH264 = 8;
+
+VideoFrame::VideoFrame()
+    : video_frame_buffer_(nullptr),
+      timestamp_rtp_(0),
+      ntp_time_ms_(0),
+      timestamp_us_(0),
+      rotation_(kVideoRotation_0) {}
 
 VideoFrame::VideoFrame(const rtc::scoped_refptr<VideoFrameBuffer>& buffer,
                        webrtc::VideoRotation rotation,
@@ -52,6 +59,10 @@
   return video_frame_buffer_ ? video_frame_buffer_->height() : 0;
 }
 
+bool VideoFrame::IsZeroSize() const {
+  return !video_frame_buffer_;
+}
+
 rtc::scoped_refptr<VideoFrameBuffer> VideoFrame::video_frame_buffer() const {
   return video_frame_buffer_;
 }