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diff --git a/media/mp4/offset_byte_queue.h b/media/mp4/offset_byte_queue.h
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+++ b/media/mp4/offset_byte_queue.h
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+// Copyright (c) 2012 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_MP4_OFFSET_BYTE_QUEUE_H_
+#define MEDIA_MP4_OFFSET_BYTE_QUEUE_H_
+
+#include "base/basictypes.h"
+#include "media/base/byte_queue.h"
+#include "media/base/media_export.h"
+
+namespace media {
+
+// A wrapper around a ByteQueue which maintains a notion of a
+// monotonically-increasing offset. All buffer access is done by passing these
+// offsets into this class, going some way towards preventing the proliferation
+// of many different meanings of "offset", "head", etc.
+class MEDIA_EXPORT OffsetByteQueue {
+ public:
+  OffsetByteQueue();
+  ~OffsetByteQueue();
+
+  // These work like their underlying ByteQueue counterparts.
+  void Reset();
+  void Push(const uint8* buf, int size);
+  void Peek(const uint8** buf, int* size);
+  void Pop(int count);
+
+  // Sets |buf| to point at the first buffered byte corresponding to |offset|,
+  // and |size| to the number of bytes available starting from that offset.
+  //
+  // It is an error if the offset is before the current head. It's not an error
+  // if the current offset is beyond tail(), but you will of course get back
+  // a null |buf| and a |size| of zero.
+  void PeekAt(int64 offset, const uint8** buf, int* size);
+
+  // Marks the bytes up to (but not including) |max_offset| as ready for
+  // deletion. This is relatively inexpensive, but will not necessarily reduce
+  // the resident buffer size right away (or ever).
+  //
+  // Returns true if the full range of bytes were successfully trimmed,
+  // including the case where |max_offset| is less than the current head.
+  // Returns false if |max_offset| > tail() (although all bytes currently
+  // buffered are still cleared).
+  bool Trim(int64 max_offset);
+
+  // The head and tail positions, in terms of the file's absolute offsets.
+  // tail() is an exclusive bound.
+  int64 head() { return head_; }
+  int64 tail() { return head_ + size_; }
+
+ private:
+  // Synchronize |buf_| and |size_| with |queue_|.
+  void Sync();
+
+  ByteQueue queue_;
+  const uint8* buf_;
+  int size_;
+  int64 head_;
+
+  DISALLOW_COPY_AND_ASSIGN(OffsetByteQueue);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_MP4_MP4_STREAM_PARSER_H_