Have content/ create and destroy its own threads.

content/shell/shell_browser_main.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_SHELL_SHELL_BROWSER_MAIN_H_
 #define CONTENT_SHELL_SHELL_BROWSER_MAIN_H_
 #pragma once
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "content/public/browser/browser_main_parts.h"
 
 class ResourceDispatcherHost;
 
 namespace base {
 class Thread;
 }
 
 namespace ui {
 class Clipboard;
 }
 
 namespace content {
 
+class IOThreadDelegate;
 class ShellBrowserContext;
 struct MainFunctionParams;
 
 class ShellBrowserMainParts : public BrowserMainParts {
  public:
   explicit ShellBrowserMainParts(const content::MainFunctionParams& parameters);
   virtual ~ShellBrowserMainParts();
 
   virtual void PreEarlyInitialization() OVERRIDE {}
   virtual void PostEarlyInitialization() OVERRIDE {}
   virtual void PreMainMessageLoopStart() OVERRIDE {}
   virtual void ToolkitInitialized() OVERRIDE {}
   virtual void PostMainMessageLoopStart() OVERRIDE {}
-  virtual void PreMainMessageLoopRun() OVERRIDE;
+  virtual content::IOThreadDelegate* PreMainMessageLoopRun() OVERRIDE;
+  virtual void PreMainMessageLoopRunThreadsCreated() OVERRIDE {}
   virtual bool MainMessageLoopRun(int* result_code) OVERRIDE;
-  virtual void PostMainMessageLoopRun() {}
+  virtual void PostMainMessageLoopRun() OVERRIDE;
+  virtual void PreStopThread(BrowserThread::ID id) OVERRIDE;
+  virtual void PostStopThread(BrowserThread::ID) OVERRIDE {}
+  virtual void FinalCleanup() OVERRIDE {}
 
   ResourceDispatcherHost* GetResourceDispatcherHost();
   ui::Clipboard* GetClipboard();
 
-  base::Thread* io_thread() { return io_thread_.get(); }
-  base::Thread* file_thread() { return file_thread_.get(); }
-
  private:
   scoped_ptr<ShellBrowserContext> browser_context_;
 
   scoped_ptr<ResourceDispatcherHost> resource_dispatcher_host_;
   scoped_ptr<ui::Clipboard> clipboard_;
 
-  scoped_ptr<base::Thread> io_thread_;
-  scoped_ptr<base::Thread> file_thread_;
-  scoped_ptr<base::Thread> db_thread_;
-  scoped_ptr<base::Thread> process_launcher_thread_;
-  scoped_ptr<base::Thread> cache_thread_;
-
   DISALLOW_COPY_AND_ASSIGN(ShellBrowserMainParts);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_SHELL_SHELL_BROWSER_MAIN_H_