Further code review changes for issue 8341027.

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;
 
+  const DOMWrapperBase._empty() : this._ptr = null;
+
   DOMWrapperBase._wrap(this._ptr) {
-        // We should never be creating duplicate wrappers.
-        assert(_ptr.dartObjectLocalStorage === null);
-        _ptr.dartObjectLocalStorage = this;
+    // We should never be creating duplicate wrappers.
+    assert(_ptr.dartObjectLocalStorage === null);
+    _ptr.dartObjectLocalStorage = this;
   }
 }