Implement measurement using futures

client/html/src/DOMWrapperBase.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 class DOMWrapperBase {
   final _ptr;
 
   DOMWrapperBase._wrap(this._ptr) {
         // We should never be creating duplicate wrappers.
         assert(_ptr.dartObjectLocalStorage === null);
         _ptr.dartObjectLocalStorage = this;
   }
 }
 
+/** This function is provided for unittest purposes only. */
+unwrapDomObject(DOMWrapperBase wrapper) {
+  return wrapper._ptr;
+}