Fix a crash when dns prefetching was being shut down without being started....

chrome/browser/net/dns_global.h

 // Copyright (c) 2006-2008 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 is the global interface for the dns prefetch services.  It centralizes
 // initialization, along with all the callbacks etc. to connect to the browser
 // process.  This allows the more standard DNS prefetching services, such as
 // provided by DnsMaster to be left as more generally usable code, and possibly
 // be shared across multiple client projects.
 
 #ifndef CHROME_BROWSER_NET_DNS_GLOBAL_H_
 #define CHROME_BROWSER_NET_DNS_GLOBAL_H_
 
 #include "chrome/browser/net/dns_master.h"
 
 #include <string>
 
 class PrefService;
 
 namespace chrome_browser_net {
 
 // Initialize dns prefetching subsystem. Must be called before any other
 // functions.
 void InitDnsPrefetch(PrefService* user_prefs);
 
-// Cancel pending lookup requests and don't make new ones.
-void ShutdownDnsPrefetch();
+// Cancel pending lookup requests and don't make new ones. Does nothing
+// if dns prefetching has not been initialized (to simplify its usage).
+void EnsureDnsPrefetchShutdown();
 
 // Free all resources allocated by InitDnsPrefetch. After that you must not call
 // any function from this file.
 void FreeDnsPrefetchResources();
 
 //------------------------------------------------------------------------------
 // Global APIs relating to Prefetching in browser
 void EnableDnsPrefetch(bool enable);
 void RegisterPrefs(PrefService* local_state);
 void RegisterUserPrefs(PrefService* user_prefs);
@@ skipping 28 matching lines @@
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(DnsPrefetcherInit);
 };
 
 }  // namespace chrome_browser_net
 
 #endif  // CHROME_BROWSER_NET_DNS_GLOBAL_H_