Create a secondary file thread, FILE_USER_BLOCKING...

chrome/browser/browser_process.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.
 
 // This interface is for managing the global services of the application. Each
 // service is lazily created when requested the first time. The service getters
 // will return NULL if the service is not available, so callers must check for
 // this condition.
 
 #ifndef CHROME_BROWSER_BROWSER_PROCESS_H_
@@ skipping 106 matching lines @@
 
   // Returns the thread that we perform I/O coordination on (network requests,
   // communication with renderers, etc.
   // NOTE: You should ONLY use this to pass to IPC or other objects which must
   // need a MessageLoop*.  If you just want to post a task, use
   // BrowserThread::PostTask (or other variants) as they take care of checking
   // that a thread is still alive, race conditions, lifetime differences etc.
   // If you still must use this check the return value for NULL.
   virtual IOThread* io_thread() = 0;
 
+  // Returns the thread used for file system operations that block user
+  // interactions. Responsiveness of this thread affect users.
+  virtual base::Thread* file_user_blocking_thread() = 0;

[jam, 2011/11/29 17:31:09]

Joi is actually planning on removing the base::Thread getters for threads in
BrowserThread (since it interfers with having BrowserThread just be an interface
that content provides). It looks like this isn't needed, so please remove it

[michaeln, 2011/11/29 21:05:28]

Done.

+
   // Returns the thread that we perform random file operations on. For code
   // that wants to do I/O operations (not network requests or even file: URL
   // requests), this is the thread to use to avoid blocking the UI thread.
   // It might be nicer to have a thread pool for this kind of thing.
   virtual base::Thread* file_thread() = 0;
 
   // Returns the thread that is used for database operations such as the web
   // database. History has its own thread since it has much higher traffic.
   virtual base::Thread* db_thread() = 0;
 
@@ skipping 91 matching lines @@
 
   virtual CRLSetFetcher* crl_set_fetcher() = 0;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(BrowserProcess);
 };
 
 extern BrowserProcess* g_browser_process;
 
 #endif  // CHROME_BROWSER_BROWSER_PROCESS_H_