Web Inspector: count DOM storage cache memory for native snapshot

content/renderer/dom_storage/webstoragearea_impl.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 "content/renderer/dom_storage/webstoragearea_impl.h"
 
 #include "base/lazy_instance.h"
 #include "base/metrics/histogram.h"
 #include "base/time.h"
 #include "base/utf_string_conversions.h"
@@ skipping 58 matching lines @@
 }
 
 void WebStorageAreaImpl::removeItem(
     const WebString& key, const WebURL& page_url) {
   cached_area_->RemoveItem(connection_id_, key, page_url);
 }
 
 void WebStorageAreaImpl::clear(const WebURL& page_url) {
   cached_area_->Clear(connection_id_, page_url);
 }
+
+size_t WebStorageAreaImpl::memoryBytesUsedByCache() const {
+  return cached_area_->MemoryBytesUsedByCache();
+}