Undo bad change in Maps class. Fix test.

tests/corelib/maps_test.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 maps_test;
 import 'dart:collection';
 
 main() {
   final key1 = "key1";
   final key2 = "key2";
@@ skipping 92 matching lines @@
   Expect.equals(true, other_map.containsKey(key1));
   Expect.equals(true, other_map.containsKey(key2));
   Expect.equals(true, other_map.containsValue(value1));
   Expect.equals(true, other_map.containsValue(value2));
   Expect.equals(2, Maps.length(other_map));
 
   // Test Collection.values.
   void testForEachCollection(value) {
     other_map[value] = value;
   }
-  Collection values = Maps.getValues(map);
+  Iterable values = Maps.getValues(map);
   other_map = new Map();
   values.forEach(testForEachCollection);
   Expect.equals(true, !other_map.containsKey(key1));
   Expect.equals(true, !other_map.containsKey(key2));
   Expect.equals(true, !other_map.containsValue(key1));
   Expect.equals(true, !other_map.containsValue(key2));
   Expect.equals(true, other_map.containsKey(value1));
   Expect.equals(true, other_map.containsKey(value2));
   Expect.equals(true, other_map.containsValue(value1));
   Expect.equals(true, other_map.containsValue(value2));
   Expect.equals(2, other_map.length);
   other_map.clear();
 
   // Test Map.putIfAbsent.
   map.clear();
   Expect.equals(false, Maps.containsKey(map, key1));
   Maps.putIfAbsent(map, key1, () => 10);
   Expect.equals(true, map.containsKey(key1));
   Expect.equals(10, map[key1]);
   Expect.equals(10, Maps.putIfAbsent(map, key1, () => 11));
 }