Fix dartc in optimized mode (broken in r3358).

corelib/src/implementation/hash_map_set.dart

Index: corelib/src/implementation/hash_map_set.dart
diff --git a/corelib/src/implementation/hash_map_set.dart b/corelib/src/implementation/hash_map_set.dart
index caea8659e6c5e07736efddd622fcad19394e6b01..a05f9f5a4a6374b73189b5411dbef045f7f8e3a1 100644
--- a/corelib/src/implementation/hash_map_set.dart
+++ b/corelib/src/implementation/hash_map_set.dart
@@ -228,8 +228,9 @@ class HashMapImplementation<K extends Hashable, V> implements HashMap<K, V> {
   void forEach(void f(K key, V value)) {
     int length = _keys.length;
     for (int i = 0; i < length; i++) {
-      if ((_keys[i] !== null) && (_keys[i] !== _DELETED_KEY)) {
-        f(_keys[i], _values[i]);
+      K key = _keys[i];
+      if ((key !== null) && (key !== _DELETED_KEY)) {
+        f(key, _values[i]);
       }
     }
   }
@@ -260,7 +261,8 @@ class HashMapImplementation<K extends Hashable, V> implements HashMap<K, V> {
   bool containsValue(V value) {
     int length = _values.length;
     for (int i = 0; i < length; i++) {
-      if ((_keys[i] !== null) && (_keys[i] !== _DELETED_KEY)) {
+      K key = _keys[i];
+      if ((key !== null) && (key !== _DELETED_KEY)) {
         if (_values[i] == value) return true;
       }
     }