**STILLBAKING** Decouple disk cache tests from backends.

net/base/cache_type.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 NET_BASE_CACHE_TYPE_H_
 #define NET_BASE_CACHE_TYPE_H_
 
 namespace net {
 
 // The types of caches that can be created.
 enum CacheType {
   DISK_CACHE,  // Disk is used as the backing storage.
   MEMORY_CACHE,  // Data is stored only in memory.
   MEDIA_CACHE,  // Optimized to handle media files.
   APP_CACHE,  // Backing store for an AppCache.
   SHADER_CACHE, // Backing store for the GL shader cache.
   PNACL_CACHE, // Backing store the PNaCl translation cache
 };
 
 // The types of disk cache backend, only used at backend instantiation.
 enum BackendType {
   CACHE_BACKEND_DEFAULT,
-  CACHE_BACKEND_BLOCKFILE,  // The |BackendImpl|.
-  CACHE_BACKEND_SIMPLE  // The |SimpleBackendImpl|.
+  CACHE_BACKEND_BLOCKFILE,
+  CACHE_BACKEND_SIMPLE,
+  CACHE_BACKEND_MEMORY,
 };
 
 }  // namespace disk_cache
 
 #endif  // NET_BASE_CACHE_TYPE_H_