Fix all for-in warnings in dart2js

pkg/compiler/lib/src/util/util.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.
 
 library dart2js.util;
 
 import 'util_implementation.dart';
 import 'characters.dart';
+import 'dart:collection' show IterableMixin;

[Siggi Cherem (dart-lang), 2016/03/12 00:40:19]

drop

[sra1, 2016/03/12 00:44:20]

Done.

 
 export 'setlet.dart';
 export 'maplet.dart';
 export 'emptyset.dart';
 
 part 'indentation.dart';
 part 'link.dart';
 
 /// Helper functions for creating hash codes.
 class Hashing {
@@ skipping 198 matching lines @@
   if (usedNames.contains(suggestedName)) {
     int counter = 0;
     while (usedNames.contains(result)) {
       counter++;
       result = "$suggestedName$counter";
     }
   }
   usedNames.add(result);
   return result;
 }