Reland of Move MutableDataY{,U,V} methods to I420Buffer only.

webrtc/common_video/video_frame_buffer.cc

Index: webrtc/common_video/video_frame_buffer.cc
diff --git a/webrtc/common_video/video_frame_buffer.cc b/webrtc/common_video/video_frame_buffer.cc
index 2d7e7f45653f98585026adc3044b1478d3ee1f87..dbb2743db1265890f4c7a3a854b6a415d059ee98 100644
--- a/webrtc/common_video/video_frame_buffer.cc
+++ b/webrtc/common_video/video_frame_buffer.cc
@@ -30,19 +30,6 @@
 }
 
 }  // namespace
-
-uint8_t* VideoFrameBuffer::MutableDataY() {
-  RTC_NOTREACHED();
-  return nullptr;
-}
-uint8_t* VideoFrameBuffer::MutableDataU() {
-  RTC_NOTREACHED();
-  return nullptr;
-}
-uint8_t* VideoFrameBuffer::MutableDataV() {
-  RTC_NOTREACHED();
-  return nullptr;
-}
 
 VideoFrameBuffer::~VideoFrameBuffer() {}