Add "contains" method to Collection.

lib/html/templates/html/impl/impl_NodeList.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(nweiz): when all implementations we target have the same name for the
 // coreimpl implementation of List<E>, extend that rather than wrapping.
 class _ListWrapper<E> implements List<E> {
   List _list;
 
   _ListWrapper(List this._list);
 
   Iterator<E> iterator() => _list.iterator();
 
+  bool contains(E element) => _list.contains(element);
+
   void forEach(void f(E element)) => _list.forEach(f);
 
   Collection map(f(E element)) => _list.map(f);
 
   List<E> filter(bool f(E element)) => _list.filter(f);
 
   bool every(bool f(E element)) => _list.every(f);
 
   bool some(bool f(E element)) => _list.some(f);
 
@@ skipping 95 matching lines @@
   }
 
   void clear() {
     _parent.text = '';
   }
 
   void operator []=(int index, _NodeImpl value) {
     _parent.$dom_replaceChild(value, this[index]);
   }
 
+  bool contains(Node element) => _Collections.contains(this, element);
+
   void forEach(void f(Node element)) => _Collections.forEach(this, f);
 
   Collection map(f(Node element)) => _Collections.map(this, [], f);
 
   Collection<Node> filter(bool f(Node element)) =>
      new _NodeListWrapper(_Collections.filter(this, <Node>[], f));
 
   bool every(bool f(Node element)) => _Collections.every(this, f);
 
   bool some(bool f(Node element)) => _Collections.some(this, f);
@@ skipping 25 matching lines @@
   void insertRange(int start, int rangeLength, [Node initialValue]) {
     throw new UnsupportedOperationException("Cannot insertRange on immutable List.");
   }
   List<Node> getRange(int start, int rangeLength) =>
     new _NodeListWrapper(_Lists.getRange(this, start, rangeLength, <Node>[]));
 
   // -- end List<Node> mixins.
 
 $!MEMBERS
 }