Make use of __proto__ when available.

sdk/lib/_internal/compiler/js_lib/js_mirrors.dart

 // Copyright (c) 2013, 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.
 
 library dart._js_mirrors;
 
 import 'dart:_js_embedded_names' show
     ALL_CLASSES,
     LAZIES,
     LIBRARIES,
@@ skipping 2216 matching lines @@
     String cacheName = Primitives.mirrorFunctionCacheName;
     JsMethodMirror cachedFunction;
     // TODO(ahe): Restore caching.
     //= JS('JsMethodMirror|Null', r'#.constructor[#]', reflectee, cacheName);
     if (cachedFunction != null) return cachedFunction;
     disableTreeShaking();
     // TODO(ahe): What about optional parameters (named or not).
     String callPrefix = "${JS_GET_NAME("CALL_PREFIX")}\$";
     var extractCallName = JS('', r'''
 function(reflectee) {
-  for (var property in reflectee) {
+  var properties = Object.keys(reflectee.constructor.prototype);
+  for (var i = 0; i < properties.length; i++) {
+    var property = properties[i];
     if (# == property.substring(0, #) &&
         property[#] >= '0' &&
         property[#] <= '9') return property;
   }
   return null;
 }
 ''', callPrefix, callPrefix.length, callPrefix.length, callPrefix.length);
     String callName = JS('String|Null', '#(#)', extractCallName, reflectee);
     if (callName == null) {
       throw new RuntimeError('Cannot find callName on "$reflectee"');
@@ skipping 777 matching lines @@
   // have a part (following a '.') that starts with '_'.
   const int UNDERSCORE = 0x5f;
   if (name.isEmpty) return true;
   int index = -1;
   do {
     if (name.codeUnitAt(index + 1) == UNDERSCORE) return false;
     index = name.indexOf('.', index + 1);
   } while (index >= 0 && index + 1 < name.length);
   return true;
 }