Add optional arguments to our indexOf/lastIndexOf methods.

client/html/src/ElementWrappingImplementation.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.
 
 // TODO(jacobr): use Lists.dart to remove some of the duplicated functionality.
 class _ChildrenElementList implements ElementList {
   // Raw Element.
   final _element;
   final _childElements;
 
@@ skipping 100 matching lines @@
   }
 
   void insertRange(int start, int length, [initialValue = null]) {
     throw const NotImplementedException();
   }
 
   List getRange(int start, int length) {
     throw const NotImplementedException();
   }
 
-  int indexOf(Element element, int startIndex) {
-    return _Lists.indexOf(this, element, startIndex, this.length);
+  int indexOf(Element element, [int start = 0]) {
+    return _Lists.indexOf(this, element, start, this.length);
   }
 
-  int lastIndexOf(Element element, int startIndex) {
-    return _Lists.lastIndexOf(this, element, startIndex);
+  int lastIndexOf(Element element, [int start = null]) {
+    if (start === null) start = length - 1;
+    return _Lists.lastIndexOf(this, element, start);
   }
 
   void clear() {
     // It is unclear if we want to keep non element nodes?
     _element.textContent = '';
   }
 
   Element removeLast() {
     final last = this.last();
     if (last != null) {
@@ skipping 86 matching lines @@
   }
 
   void insertRange(int start, int length, [initialValue = null]) {
     throw const NotImplementedException();
   }
 
   List getRange(int start, int length) {
     throw const NotImplementedException();
   }
 
-  int indexOf(Element element, int startIndex) {
+  int indexOf(Element element, [int start = 0]) {
     throw 'Not impl yet. todo(jacobr)';
   }
 
-  int lastIndexOf(Element element, int startIndex) {
+  int lastIndexOf(Element element, [int start = null]) {
     throw 'Not impl yet. todo(jacobr)';
   }
 
   void clear() {
     throw 'Not impl yet. todo(jacobr)';
   }
 
   Element removeLast() {
     throw 'Not impl yet. todo(jacobr)';
   }
@@ skipping 401 matching lines @@
     return _ptr.webkitMatchesSelector(selectors);
   }
 
   ElementEvents get on() {
     if (_on === null) {
       _on = new ElementEventsImplementation._wrap(_ptr);
     }
     return _on;
   }
 }