Add optional arguments to our indexOf/lastIndexOf methods.

runtime/lib/string.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.
 
 /**
  * [StringBase] contains common methods used by concrete String implementations,
  * e.g., OneByteString.
  */
 class StringBase {
 
@@ skipping 85 matching lines @@
   }
 
   bool endsWith(String other) {
     return this.substringMatches(this.length - other.length, other);
   }
 
   bool startsWith(String other) {
     return this.substringMatches(0, other);
   }
 
-  int indexOf(String other, int startIndex) {
+  int indexOf(String other, [int start = 0]) {
     if (other.isEmpty()) {
-      return startIndex < this.length ? startIndex : this.length;
+      return start < this.length ? start : this.length;
     }
-    if ((startIndex < 0) || (startIndex >= this.length)) {
+    if ((start < 0) || (start >= this.length)) {
       return -1;
     }
     int len = this.length - other.length + 1;
-    for (int index = startIndex; index < len; index++) {
+    for (int index = start; index < len; index++) {
       if (this.substringMatches(index, other)) {
         return index;
       }
     }
     return -1;
   }
 
-  int lastIndexOf(String other, int fromIndex) {
+  int lastIndexOf(String other, [int start = null]) {
+    if (start == null) start = length - 1;
     if (other.isEmpty()) {
-      return Math.min(this.length, fromIndex);
+      return Math.min(this.length, start);
     }
-    if (fromIndex >= this.length) {
-      fromIndex = this.length - 1;
+    if (start >= this.length) {
+      start = this.length - 1;
     }
-    for (int index = fromIndex; index >= 0; index--) {
+    for (int index = start; index >= 0; index--) {
       if (this.substringMatches(index, other)) {
         return index;
       }
     }
     return -1;
   }
 
   String substring(int startIndex, [int endIndex]) {
     if (endIndex === null) endIndex = this.length;
 
@@ skipping 295 matching lines @@
     for (int g in groups) {
       result.add(group(g));
     }
     return result;
   }
 
   final int _start;
   final String str;
   final String pattern;
 }