Undo bad change in Maps class. Fix test.

sdk/lib/collection/maps.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 dart.collection;
 
 /*
  * Helper class which implements complex [Map] operations
  * in term of basic ones ([Map.keys], [Map.operator []],
  * [Map.operator []=] and [Map.remove].)  Not all methods are
@@ skipping 27 matching lines @@
     return v;
   }
 
   static clear(Map map) {
     for (final k in map.keys.toList()) {
       map.remove(k);
     }
   }
 
   static forEach(Map map, void f(key, value)) {
-    map.keys.forEach(f);
+    for (final k in map.keys) {
+      f(k, map[k]);
+    }
   }
 
   static Iterable getValues(Map map) {
     return map.keys.mappedBy((key) => map[key]);
   }
 
   static int length(Map map) => map.keys.length;
 
   static bool isEmpty(Map map) => map.keys.isEmpty;
 
@@ skipping 41 matching lines @@
       first = false;
       Collections._emitObject(k, result, visiting);
       result.add(': ');
       Collections._emitObject(v, result, visiting);
     });
 
     result.add('}');
     visiting.removeLast();
   }
 }