Have content/ create and destroy its own threads.

content/shell/shell_browser_main.h

Index: content/shell/shell_browser_main.h
diff --git a/content/shell/shell_browser_main.h b/content/shell/shell_browser_main.h
index 55f725a1c29e9ed7424659d25e252f5b4040a5a4..11e1675a55d1ab441c7623b9cbf00f40e7dc3b90 100644
--- a/content/shell/shell_browser_main.h
+++ b/content/shell/shell_browser_main.h
@@ -22,6 +22,7 @@ class Clipboard;
 
 namespace content {
 
+class IOThreadDelegate;
 class ShellBrowserContext;
 struct MainFunctionParams;
 
@@ -35,28 +36,23 @@ class ShellBrowserMainParts : public BrowserMainParts {
   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);
 };