Refactor FFmpegVideoDecoder to try and generalize code common to all video decoders.

media/ffmpeg/ffmpeg_util.h

Index: media/ffmpeg/ffmpeg_util.h
diff --git a/media/ffmpeg/ffmpeg_util.h b/media/ffmpeg/ffmpeg_util.h
new file mode 100644
index 0000000000000000000000000000000000000000..6799cc4bebdd6bcc8f1f447c234550c49f60e9ee
--- /dev/null
+++ b/media/ffmpeg/ffmpeg_util.h
@@ -0,0 +1,18 @@
+// Copyright (c) 2009 The Chromium Authors. All rights reserved.  Use of this
+// source code is governed by a BSD-style license that can be found in the
+// LICENSE file.
+
+#ifndef MEDIA_FFMPEG_FFMPEG_UTIL_H_
+#define MEDIA_FFMPEG_FFMPEG_UTIL_H_
+
+#include "base/time.h"
+
+struct AVRational;
+
+namespace media {
+
+base::TimeDelta ConvertTimestamp(const AVRational& time_base, int64 timestamp);
+
+}  // namespace media
+
+#endif  // MEDIA_FFMPEG_FFMPEG_UTIL_H_