Remove deprecated string features.

tests/compiler/dart2js_extra/bailout_test.dart

 // Copyright (c) 2012, 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.
 
 var myString;
 
 String ifBailout(test) {
   if (test) {
     // Share the same variable for the type inference.
     var o = myString;
@@ skipping 27 matching lines @@
     var o = myString;
     if (false) o[1] = 2;
     res = res.concat(o[i]);
   }
   return res;
 }
 
 String forInBailout() {
   var n = myString.length;
   var res = '';
-  for (int i in myString.charCodes) {
+  for (int i in myString.codeUnits) {
     var o = myString;
     if (false) o[1] = 2;
     res = res.concat(new String.fromCharCodes([i]));
   }
   return res;
 }
 
 String innerForBailout() {
   var n = myString.length;
   var res = '';
@@ skipping 151 matching lines @@
   Expect.equals('1234', doWhileBailout());
 
   Expect.equals(102334155, fibonacci(40));
 
   phiBailout();
   ifPhiBailout1(1);
   ifPhiBailout1(2);
   ifPhiBailout2(1);
   ifPhiBailout2(2);
 }