All strong mode cleaning of dart2js.

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

 // Copyright (c) 2013, 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.
 
 /**
  * The expensive map is a data structure useful for tracking down
  * excessive memory usage due to large maps. It acts as an ordinary
  * hash map, but it uses 10 times more memory (by default).
  */
 class ExpensiveMap<K, V> implements Map<K, V> {
   final List _maps;
 
   ExpensiveMap([int copies = 10]) : _maps = new List(copies) {
     assert(copies > 0);
     for (int i = 0; i < _maps.length; i++) {
       _maps[i] = new Map<K, V>();
     }
   }
 
   int get length => _maps[0].length;
   bool get isEmpty => _maps[0].isEmpty;
   bool get isNotEmpty => _maps[0].isNotEmpty;
 
   Iterable<K> get keys => _maps[0].keys;
   Iterable<V> get values => _maps[0].values;
 
-  bool containsKey(K key) => _maps[0].containsKey(key);
-  bool containsValue(V value) => _maps[0].containsValue(value);
+  bool containsKey(Object key) => _maps[0].containsKey(key);
+  bool containsValue(Object value) => _maps[0].containsValue(value);
 
-  V operator [](K key) => _maps[0][key];
+  V operator [](Object key) => _maps[0][key];
 
   void forEach(void action(K key, V value)) {
     _maps[0].forEach(action);
   }
 
   void operator []=(K key, V value) {
     for (int i = 0; i < _maps.length; i++) {
       _maps[i][key] = value;
     }
   }
@@ skipping 20 matching lines @@
   }
 
   void clear() {
     for (int i = 0; i < _maps.length; i++) {
       _maps[i].clear();
     }
   }
 
   String toString() => "expensive(${_maps[0]}x${_maps.length})";
 }