Make MediaFileUtil run on thread pool.

content/browser/fileapi/browser_file_system_helper.cc

 // 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.
 
 #include "content/browser/fileapi/browser_file_system_helper.h"
 
 #include <vector>
 #include <string>
 
 #include "base/command_line.h"
 #include "base/file_path.h"
+#include "base/threading/sequenced_worker_pool.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/common/content_switches.h"
 #include "webkit/fileapi/file_system_options.h"
 #include "webkit/quota/quota_manager.h"
 
 using content::BrowserThread;
 
 namespace {
 
 const char kChromeScheme[] = "chrome";
@@ skipping 14 matching lines @@
                    : FileSystemOptions::PROFILE_MODE_NORMAL;
   return FileSystemOptions(profile_mode, additional_allowed_schemes);
 }
 
 }  // anonymous namespace
 
 scoped_refptr<fileapi::FileSystemContext> CreateFileSystemContext(
         const FilePath& profile_path, bool is_incognito,
         quota::SpecialStoragePolicy* special_storage_policy,
         quota::QuotaManagerProxy* quota_manager_proxy) {
+  base::SequencedWorkerPool* pool = BrowserThread::GetBlockingPool();
+  base::SequencedWorkerPool::SequenceToken media_sequence_token =
+      pool->GetSequenceToken();
+
   return new fileapi::FileSystemContext(
+      pool->GetSequencedTaskRunner(media_sequence_token),

[kinuko, 2012/08/02 21:12:46]

Having this as the first argument makes me feel that this task runner is the
most important TR while it would not.

[tzik, 2012/08/03 22:29:18]

Done.

       BrowserThread::GetMessageLoopProxyForThread(BrowserThread::FILE),
       BrowserThread::GetMessageLoopProxyForThread(BrowserThread::IO),

[kinuko, 2012/08/02 21:12:46]

When we have more and more task runners this wouldn't scale well.  It could be
in a different CL but maybe we could have a separate class which returns
appropriate task runners for different purposes (Media/File/IO/etc)?
Some FileUtil/FileSystemOperation might need to handle multiple task runners and
would be nice to have some neat interface.
Mock implementation of the class just return current message loop.  Chrome
implementation could keep multiple sequence tokens and return appropriate TRs.

[tzik, 2012/08/03 22:29:18]

Done.

       special_storage_policy,
       quota_manager_proxy,
       profile_path,
       CreateBrowserFileSystemOptions(is_incognito));
 }