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

webrtc/test/fake_texture_frame.h

 /*
  *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 #ifndef WEBRTC_TEST_FAKE_TEXTURE_FRAME_H_
@@ skipping 20 matching lines @@
  public:
   FakeNativeHandleBuffer(void* native_handle, int width, int height)
       : NativeHandleBuffer(native_handle, width, height) {}
 
   ~FakeNativeHandleBuffer() {
     delete reinterpret_cast<FakeNativeHandle*>(native_handle_);
   }
 
  private:
   rtc::scoped_refptr<VideoFrameBuffer> NativeToI420Buffer() override {
-    rtc::scoped_refptr<VideoFrameBuffer> buffer(
-        I420Buffer::Create(width_, height_));
+    rtc::scoped_refptr<I420Buffer> buffer = I420Buffer::Create(width_, height_);
     int half_height = (height_ + 1) / 2;
     int half_width = (width_ + 1) / 2;
     memset(buffer->MutableDataY(), 0, height_ * width_);
     memset(buffer->MutableDataU(), 0, half_height * half_width);
     memset(buffer->MutableDataV(), 0, half_height * half_width);
     return buffer;
   }
 };
 
 }  // namespace test
 }  // namespace webrtc
 #endif  //  WEBRTC_TEST_FAKE_TEXTURE_FRAME_H_