Make ElementList return ElementLists.

client/html/src/Element.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.
 
 interface ElementList extends List<Element> {
   // TODO(jacobr): add element batch manipulation methods.
+  ElementList filter(bool f(Element element));
+
+  ElementList getRange(int start, int length);
+
   Element get first();
   // TODO(jacobr): add insertAt
 }
 
 class DeferredElementRect {
   // TODO(jacobr)
 }
 
 interface ElementEvents extends Events {
   EventListenerList get abort();
@@ skipping 171 matching lines @@
   Future<ElementRect> get rect();
 
   Future<CSSStyleDeclaration> get computedStyle();
 
   Future<CSSStyleDeclaration> getComputedStyle(String pseudoElement);
 
   ElementEvents get on();
 
   Element clone(bool deep);
 }