Revert of Delete unused and almost unused frame-related methods.

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 463e8ed44254a30829bde14e3c7bfe612b342533..bfac3a680de9fc18ace1dc323ce1b29d34655197 100644
--- a/webrtc/common_video/video_frame.cc
+++ b/webrtc/common_video/video_frame.cc
@@ -155,6 +155,20 @@
   return video_frame_buffer_;
 }
 
+void VideoFrame::set_video_frame_buffer(
+    const rtc::scoped_refptr<webrtc::VideoFrameBuffer>& buffer) {
+  RTC_DCHECK(buffer);
+  video_frame_buffer_ = buffer;
+}
+
+VideoFrame VideoFrame::ConvertNativeToI420Frame() const {
+  RTC_DCHECK(video_frame_buffer_->native_handle());
+  VideoFrame frame;
+  frame.ShallowCopy(*this);
+  frame.set_video_frame_buffer(video_frame_buffer_->NativeToI420Buffer());
+  return frame;
+}
+
 size_t EncodedImage::GetBufferPaddingBytes(VideoCodecType codec_type) {
   switch (codec_type) {
     case kVideoCodecVP8: