AppCache: Add nullptr check where AppCacheStorageImpl::disk_cache() is called

content/browser/appcache/appcache_storage_impl.h

 // Copyright (c) 2011 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 CONTENT_BROWSER_APPCACHE_APPCACHE_STORAGE_IMPL_H_
 #define CONTENT_BROWSER_APPCACHE_APPCACHE_STORAGE_IMPL_H_
 
 #include <stdint.h>
 
 #include <deque>
@@ skipping 127 matching lines @@
 
   void CallOnMainResponseFound(DelegateReferenceVector* delegates,
                                const GURL& url,
                                const AppCacheEntry& entry,
                                const GURL& namespace_entry_url,
                                const AppCacheEntry& fallback_entry,
                                int64_t cache_id,
                                int64_t group_id,
                                const GURL& manifest_url);
 
+  // Don't call this when |is_disabled_| is true.
   CONTENT_EXPORT AppCacheDiskCache* disk_cache();
 
   // The directory in which we place files in the file system.
   base::FilePath cache_directory_;
   bool is_incognito_;
 
   // This class operates primarily on the IO thread, but schedules
   // its DatabaseTasks on the db thread. Separately, the disk_cache uses
   // the cache thread.
   scoped_refptr<base::SingleThreadTaskRunner> db_thread_;
@@ skipping 28 matching lines @@
   std::deque<base::Closure> pending_simple_tasks_;
   base::WeakPtrFactory<AppCacheStorageImpl> weak_factory_;
 
   friend class content::AppCacheStorageImplTest;
   friend class content::ChromeAppCacheServiceTest;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_APPCACHE_APPCACHE_STORAGE_IMPL_H_