Always destruct url request context getter on io thread....

chrome/browser/net/url_request_context_getter.h

 // Copyright (c) 2009 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 CHROME_BROWSER_NET_URL_REQUEST_CONTEXT_GETTER_H_
 #define CHROME_BROWSER_NET_URL_REQUEST_CONTEXT_GETTER_H_
 
 #include "base/ref_counted.h"
+#include "chrome/browser/chrome_thread.h"
 
 namespace net {
 class CookieStore;
 }
 
 class URLRequestContext;
 
 // Interface for retrieving an URLRequestContext.
 class URLRequestContextGetter
-    : public base::RefCountedThreadSafe<URLRequestContextGetter> {
+    : public base::RefCountedThreadSafe<URLRequestContextGetter,
+                                        ChromeThread::DeleteOnIOThread> {
  public:
   virtual URLRequestContext* GetURLRequestContext() = 0;
 
   // Defaults to GetURLRequestContext()->cookie_store(), but
   // implementations can override it.
   virtual net::CookieStore* GetCookieStore();
 
  protected:
-  friend class base::RefCountedThreadSafe<URLRequestContextGetter>;
+  friend class ChromeThread;
+  friend class DeleteTask<URLRequestContextGetter>;
 
   virtual ~URLRequestContextGetter() {}
 };
 
 #endif  // CHROME_BROWSER_NET_URL_REQUEST_CONTEXT_GETTER_H_