Reland of New method I420Buffer::SetToBlack.

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 34213e4656ce766f5cb6f2fdc24e566c02cf152e..27aea3efc595f5a3df62114880f9a4f2432f8afd 100644
--- a/webrtc/common_video/video_frame_buffer.cc
+++ b/webrtc/common_video/video_frame_buffer.cc
@@ -200,6 +200,14 @@ rtc::scoped_refptr<I420Buffer> I420Buffer::Copy(
   return copy;
 }
 
+void I420Buffer::SetToBlack() {
+  RTC_CHECK(libyuv::I420Rect(MutableDataY(), StrideY(),
+                             MutableDataU(), StrideU(),
+                             MutableDataV(), StrideV(),
+                             0, 0, width(), height(),
+                             0, 128, 128) == 0);
+}
+
 NativeHandleBuffer::NativeHandleBuffer(void* native_handle,
                                        int width,
                                        int height)