Create a secondary file thread, FILE_USER_BLOCKING...

content/browser/browser_thread.h

 // Copyright (c) 2011 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_BROWSER_THREAD_H_
 #define CONTENT_BROWSER_BROWSER_THREAD_H_
 #pragma once
 
 #include "base/callback.h"
 #include "base/synchronization/lock.h"
@@ skipping 47 matching lines @@
 
     // This is the thread that interacts with the file system.
     FILE,
 
     // Used to launch and terminate Chrome processes.
     PROCESS_LAUNCHER,
 
     // This is the thread to handle slow HTTP cache operations.
     CACHE,
 
+    // Used to handle appcache fileio operations.
+    APPCACHE,

[rvargas (doing something else), 2011/10/21 19:46:17]

ditto: before the cache thread?

+
     // This is the thread that processes IPC and network messages.
     IO,
 
 #if defined(OS_CHROMEOS)
     // This thread runs websocket to TCP proxy.
     // TODO(dilmah): remove this thread, instead implement this functionality
     // as hooks into websocket layer.
     WEB_SOCKET_PROXY,
 #endif
 
@@ skipping 164 matching lines @@
   static base::Lock lock_;
 
   // An array of the BrowserThread objects.  This array is protected by |lock_|.
   // The threads are not owned by this array.  Typically, the threads are owned
   // on the UI thread by the g_browser_process object.  BrowserThreads remove
   // themselves from this array upon destruction.
   static BrowserThread* browser_threads_[ID_COUNT];
 };
 
 #endif  // CONTENT_BROWSER_BROWSER_THREAD_H_