fix #552, Object members on native types

tool/input_sdk/private/ddc_runtime/utils.dart

 // Copyright (c) 2015, 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.
 part of dart._runtime;
 
 /// This library defines a set of general javascript utilities for us
 /// by the Dart runtime.
 // TODO(ochafik): Rewrite some of these in Dart when possible.
 
 defineProperty(obj, name, desc) =>
     JS('', 'Object.defineProperty(#, #, #)', obj, name, desc);
 
 getOwnPropertyDescriptor(obj, name) =>
     JS('', 'Object.getOwnPropertyDescriptor(#, #)', obj, name);
 
-getOwnPropertyNames(obj) => JS('', 'Object.getOwnPropertyNames(#)', obj);
+Iterable getOwnPropertyNames(obj) =>
+    JS('', 'Object.getOwnPropertyNames(#)', obj);
 
-getOwnPropertySymbols(obj) => JS('', 'Object.getOwnPropertySymbols(#)', obj);
+Iterable getOwnPropertySymbols(obj) =>
+    JS('', 'Object.getOwnPropertySymbols(#)', obj);
 
 final hasOwnProperty = JS('', 'Object.prototype.hasOwnProperty');
 
 // TODO(ochafik): Add ES6 class syntax support to JS intrinsics to avoid this.
 final StrongModeError = JS('', '''(function() {
   function StrongModeError(message) {
     Error.call(this);
     this.message = message;
   };
   Object.setPrototypeOf(StrongModeError.prototype, Error.prototype);
@@ skipping 87 matching lines @@
 }
 
 @JSExportName('export')
 exportProperty(to, from, name) => copyProperty(to, from, name);
 
 /// Copy properties from source to destination object.
 /// This operation is commonly called `mixin` in JS.
 copyProperties(to, from) {
   return copyTheseProperties(to, from, getOwnNamesAndSymbols(from));
 }