New method I420Buffer::Copy.

Needed to replace cricket::VideoFrame::MakeExclusive in chromium.

BUG=webrtc:5682

Review URL: https://codereview.webrtc.org/1822283002

Cr-Commit-Position: refs/heads/master@{#12155}
diff --git a/webrtc/test/frame_utils.h b/webrtc/test/frame_utils.h
index 42e2cba..668d999 100644
--- a/webrtc/test/frame_utils.h
+++ b/webrtc/test/frame_utils.h
@@ -11,9 +11,11 @@
 #define WEBRTC_TEST_FRAME_UTILS_H_
 
 #include "webrtc/base/basictypes.h"
+#include "webrtc/base/scoped_ref_ptr.h"
 
 namespace webrtc {
 class VideoFrame;
+class VideoFrameBuffer;
 namespace test {
 
 bool EqualPlane(const uint8_t* data1,
@@ -24,6 +26,9 @@
 
 bool FramesEqual(const webrtc::VideoFrame& f1, const webrtc::VideoFrame& f2);
 
+bool FrameBufsEqual(const rtc::scoped_refptr<webrtc::VideoFrameBuffer>& f1,
+                    const rtc::scoped_refptr<webrtc::VideoFrameBuffer>& f2);
+
 }  // namespace test
 }  // namespace webrtc