Add warnings and hints to for-in.

pkg/compiler/lib/src/helpers/stats.dart

 // Copyright (c) 2014, 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 dart2js.helpers;
 
 // Helper methods for statistics.
 
 /// Current stats collector. Use [enableStatsOutput] to enable recording of
 /// stats.
@@ skipping 440 matching lines @@
     return other.count - count;
   }
 
   void printOn(StringBuffer sb, String indentation) {
     String countText = '$indentation$count  ';
     sb.write(countText);
     sb.write('\n');
     indentation = ''.padLeft(countText.length, ' ');
     if (commonPrefix != null) {
       int index = 0;
-      for (String line in commonPrefix) {
+      for (StackTraceLine line in commonPrefix) {
         sb.write(indentation);
         if (index > 1) {
           sb.write('...\n');
           break;
         }
         sb.write(line);
         sb.write('\n');
         index++;
       }
     }
@@ skipping 307 matching lines @@
 /// Returns a new map in which the keys of [map] are sorted using [compare].
 /// If [compare] is null, the keys must be [Comparable].
 Map sortMap(Map map, [int compare(a,b)]) {
   List keys = map.keys.toList();
   keys.sort(compare);
   Map sortedMap = new Map();
   keys.forEach((k) => sortedMap[k] = map[k]);
   return sortedMap;
 }