Added implementation of String.codeUnits.

sdk/lib/_internal/compiler/implementation/lib/js_string.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.
 
 part of _interceptors;
 
 /**
  * The interceptor class for [String]. The compiler recognizes this
  * class as an interceptor, and changes references to [:this:] to
  * actually use the receiver of the method, which is generated as an extra
@@ skipping 131 matching lines @@
   }
 
   List<int> get charCodes  {
     List<int> result = new List<int>.fixedLength(length);
     for (int i = 0; i < length; i++) {
       result[i] = JS('int', '#.charCodeAt(#)', this, i);
     }
     return result;
   }
 
-  Iterable<int> get codeUnits {
-    throw new UnimplementedError("String.codeUnits");
-  }
+  Iterable<int> get codeUnits => new CodeUnits(this);
 
   Runes get runes => new Runes(this);
 
   int indexOf(String other, [int start = 0]) {
     checkNull(other);
     if (start is !int) throw new ArgumentError(start);
     if (other is !String) throw new ArgumentError(other);
     if (start < 0) return -1;
     return JS('int', r'#.indexOf(#, #)', this, other, start);
   }
@@ skipping 53 matching lines @@
   Type get runtimeType => String;
 
   int get length => JS('int', r'#.length', this);
 
   String operator [](int index) {
     if (index is !int) throw new ArgumentError(index);
     if (index >= length || index < 0) throw new RangeError.value(index);
     return JS('String', '#[#]', this, index);
   }
 }