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

webrtc/common_video/include/video_frame_buffer.h

Index: webrtc/common_video/include/video_frame_buffer.h
diff --git a/webrtc/common_video/include/video_frame_buffer.h b/webrtc/common_video/include/video_frame_buffer.h
index 94b3d5d8330ed320c6703bcdb890dfa40b87539c..2ac1dd800639038d00b8850129a1181117976541 100644
--- a/webrtc/common_video/include/video_frame_buffer.h
+++ b/webrtc/common_video/include/video_frame_buffer.h
@@ -44,12 +44,6 @@ class VideoFrameBuffer : public rtc::RefCountInterface {
   virtual const uint8_t* DataU() const = 0;
   virtual const uint8_t* DataV() const = 0;
 
-  // TODO(nisse): Move MutableData methods to the I420Buffer subclass.
-  // Non-const data access.
-  virtual uint8_t* MutableDataY();
-  virtual uint8_t* MutableDataU();
-  virtual uint8_t* MutableDataV();
-
   // Returns the number of bytes between successive rows for a given plane.
   virtual int StrideY() const = 0;
   virtual int StrideU() const = 0;
@@ -97,9 +91,9 @@ class I420Buffer : public VideoFrameBuffer {
   const uint8_t* DataU() const override;
   const uint8_t* DataV() const override;
 
-  uint8_t* MutableDataY() override;
-  uint8_t* MutableDataU() override;
-  uint8_t* MutableDataV() override;
+  uint8_t* MutableDataY();
+  uint8_t* MutableDataU();
+  uint8_t* MutableDataV();
   int StrideY() const override;
   int StrideU() const override;
   int StrideV() const override;