Add optional arguments to our indexOf/lastIndexOf methods.

compiler/lib/implementation/string.js

Index: compiler/lib/implementation/string.js
===================================================================
--- compiler/lib/implementation/string.js	(revision 942)
+++ compiler/lib/implementation/string.js	(working copy)
@@ -18,11 +18,11 @@
   return typeof other == 'string' && this == other;
 }
 
-function native_StringImplementation_indexOf(other, startIndex) {
+function native_StringImplementation__nativeIndexOf(other, startIndex) {
   return this.indexOf(other, startIndex);
 }
 
-function native_StringImplementation_lastIndexOf(other, fromIndex) {
+function native_StringImplementation__nativeLastIndexOf(other, fromIndex) {
   if (other == "") {
     return Math.min(this.length, fromIndex);
   }