Change List constructors.

sdk/lib/core/map.dart

Index: sdk/lib/core/map.dart
diff --git a/sdk/lib/core/map.dart b/sdk/lib/core/map.dart
index 6dd0789bb0f6e3535b91bec37e4ad9f1b9923292..caad8373d9587ef44bd0588f166fbb2414fe61bf 100644
--- a/sdk/lib/core/map.dart
+++ b/sdk/lib/core/map.dart
@@ -166,7 +166,7 @@ class _HashMapImpl<K, V> implements HashMap<K, V> {
     _numberOfEntries = 0;
     _numberOfDeleted = 0;
     _loadLimit = _computeLoadLimit(_INITIAL_CAPACITY);
-    _keys = new List(_INITIAL_CAPACITY);
+    _keys = new List.fixedLength(_INITIAL_CAPACITY);
     _values = new List<V>(_INITIAL_CAPACITY);
   }
 
@@ -273,7 +273,7 @@ class _HashMapImpl<K, V> implements HashMap<K, V> {
     _loadLimit = _computeLoadLimit(newCapacity);
     List oldKeys = _keys;
     List<V> oldValues = _values;
-    _keys = new List(newCapacity);
+    _keys = new List.fixedLength(newCapacity);
     _values = new List<V>(newCapacity);
     for (int i = 0; i < capacity; i++) {
       // [key] can be either of type [K] or [_DeletedKeySentinel].