Add optional arguments to our indexOf/lastIndexOf methods.

compiler/lib/implementation/array.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 ListFactory {
   factory List<E>.from(Iterable<E> other) {
     List<E> list = new List<E>();
     for (final e in other) {
       list.add(e);
     }
@@ skipping 129 matching lines @@
 
   List<T> getRange(int start, int length) {
     if (length == 0) return [];
     Arrays.rangeCheck(this, start, length);
     List list = new List<T>();
     list.length = length;
     Arrays.copy(this, start, list, 0, length);
     return list;
   }
 
-  int indexOf(T element, int startIndex) {
-    return Arrays.indexOf(this, element, startIndex, this.length);
+  int indexOf(T element, [int start = 0]) {
+    return Arrays.indexOf(this, element, start, this.length);
   }
 
-  int lastIndexOf(T element, int startIndex) {
-    return Arrays.lastIndexOf(this, element, startIndex);
+  int lastIndexOf(T element, [int start = null]) {
+    if (start === null) start = length - 1;
+    return Arrays.lastIndexOf(this, element, start);
   }
 
   void add(T element) {
     if (_isFixed) {
       throw const UnsupportedOperationException(
           "Cannot add to a non-extendable list");
     } else {
       _add(element);
     }
   }
@@ skipping 92 matching lines @@
   }
 
   static List _newList(int len) native {
     return new List(len);
   }
 
   static void _throwIndexOutOfRangeException(int index) native {
     throw new IndexOutOfRangeException(index);
   }
 }