Don't put private members in dart:html interfaces.

client/dom/templates/html/impl/impl_Element.darttemplate

 // Copyright (c) 2012, 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.
 
 // TODO(jacobr): use _Lists.dart to remove some of the duplicated
 // functionality.
 class _ChildrenElementList implements ElementList {
   // Raw Element.
   final _ElementImpl _element;
   final _HTMLCollectionImpl _childElements;
@@ skipping 515 matching lines @@
         () => new _ElementRectImpl(this),
         new Completer<ElementRect>());
   }
 
   Future<CSSStyleDeclaration> get computedStyle() {
      // TODO(jacobr): last param should be null, see b/5045788
      return getComputedStyle('');
   }
 
   Future<CSSStyleDeclaration> getComputedStyle(String pseudoElement) {
-    return _createMeasurementFuture(() =>
-            window._getComputedStyle(this, pseudoElement),
+    return _createMeasurementFuture(
+        () => _window._getComputedStyle(this, pseudoElement),
         new Completer<CSSStyleDeclaration>());
   }
 $!MEMBERS
 }