Make SourceString Iterable<int>.

frog/leg/scanner/string_scanner.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.
 
 /**
  * Scanner that reads from a String and creates tokens that points to
  * substrings.
  */
 class StringScanner extends ArrayBasedScanner<SourceString> {
   final String string;
@@ skipping 29 matching lines @@
 
   const SubstringWrapper(String this.internalString,
                          int this.begin, int this.end);
 
   int hashCode() => toString().hashCode();
 
   bool operator ==(other) {
     return other is SourceString && toString() == other.toString();
   }
 
+  Iterator<int> iterator() =>
+      new StringCodeIterator.substring(stringValue, begin, end);
+
   int get length() => end - begin;
 
   void printOn(StringBuffer sb) {
     sb.add(this);
   }
 
   String toString() => internalString.substring(begin, end);
 
   String get stringValue() => toString();
 }