[core] cleanup === and !==

lib/coreimpl/linked_hash_map.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.
 
 /**
  * This class represents a pair of two objects, used by LinkedHashMap
  * to store a {key, value} in a list.
  */
 class KeyValuePair<K, V> {
   KeyValuePair(this.key, this.value) {}
@@ skipping 27 matching lines @@
     if (_map.containsKey(key)) {
       _map[key].element.value = value;
     } else {
       _list.addLast(new KeyValuePair<K, V>(key, value));
       _map[key] = _list.lastEntry();
     }
   }
 
   V operator [](K key) {
     DoubleLinkedQueueEntry<KeyValuePair<K, V>> entry = _map[key];
-    if (entry === null) return null;
+    if (entry == null) return null;
     return entry.element.value;
   }
 
   V remove(K key) {
     DoubleLinkedQueueEntry<KeyValuePair<K, V>> entry = _map.remove(key);
-    if (entry === null) return null;
+    if (entry == null) return null;
     entry.remove();
     return entry.element.value;
   }
 
   V putIfAbsent(K key, V ifAbsent()) {
     V value = this[key];
-    if ((this[key] === null) && !(containsKey(key))) {
+    if ((this[key] == null) && !(containsKey(key))) {
       value = ifAbsent();
       this[key] = value;
     }
     return value;
   }
 
   Collection<K> getKeys() {
     List<K> list = new List<K>(length);
     int index = 0;
     _list.forEach(void _(KeyValuePair<K, V> entry) {
@@ skipping 40 matching lines @@
 
   void clear() {
     _map.clear();
     _list.clear();
   }
 
   String toString() {
     return Maps.mapToString(this);
   }
 }