Write out CacheStorageCache size to index file.

content/browser/cache_storage/cache_storage.proto

 // Copyright 2014 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.
 
 syntax = "proto2";
 
 option optimize_for = LITE_RUNTIME;
 
 package content.proto;
 
 message CacheStorageIndex {
   message Cache {
     required string name = 1;
     optional string cache_dir = 2;
+    optional int64 size = 3;
   }
   repeated Cache cache = 1;
   optional string origin = 2;
 }
 
 message CacheHeaderMap {
   required string name = 1;
   required string value = 2;
 }
 
@@ skipping 20 matching lines @@
   optional int64 response_time = 6;
   repeated string cors_exposed_header_names = 7;
   repeated string url_list = 8;
 }
 
 message CacheMetadata {
   required CacheRequest request = 1;
   required CacheResponse response = 2;
   optional int64 entry_time = 3;
 }