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 674397020369a92b55bac8668c04a645d1c2e68c..ae7855fe86d5aa3dfcc952617eed0b89f802c376 100644
--- a/webrtc/common_video/include/video_frame_buffer.h
+++ b/webrtc/common_video/include/video_frame_buffer.h
@@ -45,12 +45,6 @@ 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;
@@ -98,9 +92,9 @@ 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;