Introduce audio/video BufferingState to Pipeline.

media/base/buffering_state.h

+// Copyright 2014 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_BASE_BUFFERING_STATE_H_
+#define MEDIA_BASE_BUFFERING_STATE_H_
+
+#include "base/callback_forward.h"
+
+namespace media {
+
+enum BufferingState {
+  // Indicates that there is no data buffered.
+  //
+  // Typical reason is data underflow and hence playback should be paused.
+  BUFFERING_HAVE_NOTHING,
+
+  // Indicates that enough data has been buffered.
+  //
+  // Typical reason is enough data has been prerolled to start playback.
+  BUFFERING_HAVE_ENOUGH,
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_BUFFERING_STATE_H_