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 0e617cade2f27f2e562ecf28c5d46921e0e92faa..ffa44e641fbab6bb63ff9799d833cd3741d6c131 100644
--- a/content/shell/shell_browser_main.h
+++ b/content/shell/shell_browser_main.h
@@ -35,28 +35,25 @@ class ShellBrowserMainParts : public BrowserMainParts {
   virtual void PreMainMessageLoopStart() OVERRIDE {}
   virtual void ToolkitInitialized() OVERRIDE {}
   virtual void PostMainMessageLoopStart() OVERRIDE {}
-  virtual void PreMainMessageLoopRun() OVERRIDE;
+  virtual void PreCreateThreads() OVERRIDE;
+  virtual void PreStartThread(BrowserThread::ID id) OVERRIDE {}
+  virtual void PostStartThread(BrowserThread::ID id) OVERRIDE {}
+  virtual void PreMainMessageLoopRun() OVERRIDE {}
   virtual bool MainMessageLoopRun(int* result_code) OVERRIDE;
-  virtual void PostMainMessageLoopRun() OVERRIDE {}
+  virtual void PostMainMessageLoopRun() OVERRIDE;
+  virtual void PreStopThread(BrowserThread::ID id) OVERRIDE;
+  virtual void PostStopThread(BrowserThread::ID) OVERRIDE {}
+  virtual void PostDestroyThreads() 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);
 };