Fix some cases where Map.containsValue did not accept Object as argument.

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;
 
 /**
  * Base class for implementing a [Map].
  *
  * This class has a basic implementation of all but five of the members of
@@ skipping 42 matching lines @@
       action(key, this[key]);
     }
   }
 
   void addAll(Map<K, V> other) {
     for (K key in other.keys) {
       this[key] = other[key];
     }
   }
 
-  bool containsValue(V value) {
+  bool containsValue(Object value) {
     for (K key in keys) {
       if (this[key] == value) return true;
     }
     return false;
   }
 
   V putIfAbsent(K key, V ifAbsent()) {
     if (keys.contains(key)) {
       return this[key];
     }
@@ skipping 137 matching lines @@
 class UnmodifiableMapView<K, V> =
     MapView<K, V> with _UnmodifiableMapMixin<K, V>;
 
 /**
  * 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
  * necessary to implement each particular operation.
  */
 class Maps {
-  static bool containsValue(Map map, value) {
+  static bool containsValue(Map map, Object value) {
     for (final v in map.values) {
-      if (value == v) {
+      if (v == value) {
         return true;
       }
     }
     return false;
   }
 
-  static bool containsKey(Map map, key) {
+  static bool containsKey(Map map, Object key) {
     for (final k in map.keys) {
-      if (key == k) {
+      if (k == key) {
         return true;
       }
     }
     return false;
   }
 
   static putIfAbsent(Map map, key, ifAbsent()) {
     if (map.containsKey(key)) {
       return map[key];
     }
@@ skipping 101 matching lines @@
       map[keyIterator.current] = valueIterator.current;
       hasNextKey = keyIterator.moveNext();
       hasNextValue = valueIterator.moveNext();
     }
 
     if (hasNextKey || hasNextValue) {
       throw new ArgumentError("Iterables do not have same length.");
     }
   }
 }