Do not set growable array length unnecessarily.

runtime/lib/growable_array.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.
 
 class _GrowableObjectArray<T> implements List<T> {
   factory _GrowableObjectArray._uninstantiable() {
     throw new UnsupportedError(
         "GrowableObjectArray can only be allocated by the VM");
   }
 
@@ skipping 110 matching lines @@
     if (start == end) return <T>[];
     List list = new _GrowableObjectArray<T>.withCapacity(length);
     list.length = length;
     Arrays.copy(this, start, list, 0, length);
     return list;
   }
 
   factory _GrowableObjectArray(int length) {
     var data = new _ObjectArray((length == 0) ? 4 : length);
     var result = new _GrowableObjectArray<T>.withData(data);
-    result._setLength(length);
+    if (length > 0) {
+      result._setLength(length);
+    }
     return result;
   }
 
   factory _GrowableObjectArray.withCapacity(int capacity) {
     var data = new _ObjectArray((capacity == 0)? 4 : capacity);
     return new _GrowableObjectArray<T>.withData(data);
   }
 
   factory _GrowableObjectArray.from(Iterable<T> other) {
     List<T> result = new _GrowableObjectArray<T>();
@@ skipping 205 matching lines @@
   }
 
   Set<T> toSet() {
     return new Set<T>.from(this);
   }
 
   Map<int, T> asMap() {
     return IterableMixinWorkaround.asMapList(this);
   }
 }