New helper function test::ReadI420Buffer, refactor FrameReader to use it.

webrtc/test/frame_utils.h

Index: webrtc/test/frame_utils.h
diff --git a/webrtc/test/frame_utils.h b/webrtc/test/frame_utils.h
index aef3c9ff2af201fb6dd272a75b6a8973ad6f4c20..28a7e4592500f8bfee876938e86d30960d15fe2b 100644
--- a/webrtc/test/frame_utils.h
+++ b/webrtc/test/frame_utils.h
@@ -14,6 +14,7 @@
 #include "webrtc/base/scoped_ref_ptr.h"
 
 namespace webrtc {
+class I420Buffer;
 class VideoFrame;
 class VideoFrameBuffer;
 namespace test {
@@ -38,6 +39,8 @@ 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);
 
+rtc::scoped_refptr<I420Buffer> ReadI420Buffer(int width, int height, FILE *);
+
 }  // namespace test
 }  // namespace webrtc