Purge in-memory localStorage areas if the # of areas exceeds the limit

webkit/dom_storage/dom_storage_area.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 "webkit/dom_storage/dom_storage_area.h"
 
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
@@ skipping 374 matching lines @@
     bool success = backing_->CommitChanges(
         commit_batch_->clear_all_first,
         commit_batch_->changed_values);
     DCHECK(success);
   }
   commit_batch_.reset();
   backing_.reset();
   session_storage_backing_ = NULL;
 }
 
+size_t DomStorageArea::GetMapSize() const {
+  return map_->bytes_used();
+}
+
 }  // namespace dom_storage