Add optional arguments to our indexOf/lastIndexOf methods.

client/html/src/NodeWrappingImplementation.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 _ChildrenNodeList implements NodeList {
   // Raw node.
   final _node;
   final _childNodes;
 
   _ChildrenNodeList._wrap(var node)
@@ skipping 103 matching lines @@
   }
 
   void insertRange(int start, int length, [initialValue = null]) {
     throw const NotImplementedException();
   }
 
   List getRange(int start, int length) {
     throw const NotImplementedException();
   }
 
-  int indexOf(Node element, int startIndex) {
-    return _Lists.indexOf(this, element, startIndex, this.length);
+  int indexOf(Node element, [int start = 0]) {
+    return _Lists.indexOf(this, element, start, this.length);
   }
 
-  int lastIndexOf(Node element, int startIndex) {
-    return _Lists.lastIndexOf(this, element, startIndex);
+  int lastIndexOf(Node element, [int start = null]) {
+    if (start === null) start = length - 1;
+    return _Lists.lastIndexOf(this, element, start);
   }
 
   void clear() {
     _node.textContent = '';
   }
 
   Node removeLast() {
     final last = this.last();
     if (last != null) {
       _node.removeChild(LevelDom.unwrap(last));
@@ skipping 68 matching lines @@
   // array.
   Node insertBefore(Node newChild, Node refChild) {
     return LevelDom.wrapNode(_ptr.insertBefore(
         LevelDom.unwrap(newChild), LevelDom.unwrap(refChild)));
   }
 
   Node clone(bool deep) {
     return LevelDom.wrapNode(_ptr.cloneNode(deep));
   }
 }