Use ByteStream in downloads system to decouple source and sink.

content/browser/download/download_buffer.h

-// 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 CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_BUFFER_H_
-#define CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_BUFFER_H_
-#pragma once
-
-#include <vector>
-
-#include "base/memory/ref_counted.h"
-#include "base/synchronization/lock.h"
-#include "content/common/content_export.h"
-
-namespace net {
-class IOBuffer;
-}
-
-namespace content {
-
-typedef std::pair<scoped_refptr<net::IOBuffer>, size_t> ContentElement;
-typedef std::vector<ContentElement> ContentVector;
-
-// Helper function for ContentVector.
-// Assembles the data from |contents| and returns it in an |IOBuffer|.
-// The number of bytes in the |IOBuffer| is returned in |*num_bytes|
-// (if |num_bytes| is not NULL).
-// If |contents| is empty, returns NULL as an |IOBuffer| is not allowed
-// to have 0 bytes.
-CONTENT_EXPORT net::IOBuffer* AssembleData(const ContentVector& contents,
-                                           size_t* num_bytes);
-
-// |DownloadBuffer| is a thread-safe wrapper around |ContentVector|.
-//
-// It is created and populated on the IO thread, and passed to the
-// FILE thread for writing. In order to avoid flooding the FILE thread with
-// too many small write messages, each write is appended to the
-// |DownloadBuffer| while waiting for the task to run on the FILE
-// thread. Access to the write buffers is synchronized via the lock.
-class CONTENT_EXPORT DownloadBuffer
-    : public base::RefCountedThreadSafe<DownloadBuffer> {
- public:
-  DownloadBuffer();
-
-  // Adds data to the buffers.
-  // Returns the number of |IOBuffer|s in the ContentVector.
-  size_t AddData(net::IOBuffer* io_buffer, size_t byte_count);
-
-  // Retrieves the ContentVector of buffers, clearing the contents.
-  // The caller takes ownership.
-  ContentVector* ReleaseContents();
-
-  // Gets the number of |IOBuffers| we have.
-  size_t size() const;
-
- private:
-  friend class base::RefCountedThreadSafe<DownloadBuffer>;
-
-  // Do not allow explicit destruction by anyone else.
-  ~DownloadBuffer();
-
-  mutable base::Lock lock_;
-  ContentVector contents_;
-
-  DISALLOW_COPY_AND_ASSIGN(DownloadBuffer);
-};
-
-}  // namespace content
-
-#endif  // CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_BUFFER_H_