Fix NULL pointer access

chrome/browser/extensions/extension_system.cc

 // Copyright (c) 2012 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.
 
 #include "chrome/browser/extensions/extension_system.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/file_path.h"
 #include "base/string_tokenizer.h"
@@ skipping 45 matching lines @@
 
 //
 // ExtensionSystemImpl::Shared
 //
 
 ExtensionSystemImpl::Shared::Shared(Profile* profile)
     : profile_(profile) {
 }
 
 ExtensionSystemImpl::Shared::~Shared() {
-  rules_registry_service_->Shutdown();
+  if (rules_registry_service_.get())
+    rules_registry_service_->Shutdown();
 }
 
 void ExtensionSystemImpl::Shared::InitPrefs() {
   bool extensions_disabled =
       profile_->GetPrefs()->GetBoolean(prefs::kDisableExtensions) ||
       CommandLine::ForCurrentProcess()->HasSwitch(switches::kDisableExtensions);
   extension_prefs_.reset(new ExtensionPrefs(
       profile_->GetPrefs(),
       profile_->GetPath().AppendASCII(ExtensionService::kInstallDirectoryName),
       ExtensionPrefValueMapFactory::GetForProfile(profile_)));
@@ skipping 234 matching lines @@
 }
 
 void ExtensionSystemImpl::UnregisterExtensionWithRequestContexts(
     const std::string& extension_id,
     const extension_misc::UnloadedExtensionReason reason) {
   BrowserThread::PostTask(
       BrowserThread::IO, FROM_HERE,
       base::Bind(&ExtensionInfoMap::RemoveExtension, info_map(),
                  extension_id, reason));
 }