Work around Safari for-in bug.

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

Index: dart/sdk/lib/_internal/compiler/js_lib/js_names.dart
diff --git a/dart/sdk/lib/_internal/compiler/js_lib/js_names.dart b/dart/sdk/lib/_internal/compiler/js_lib/js_names.dart
index 95f7e4902e5acf094b9a1902d3c7ce0f25d03d68..73272690e1f630b1ba65aa8b0bb360e79027e593 100644
--- a/dart/sdk/lib/_internal/compiler/js_lib/js_names.dart
+++ b/dart/sdk/lib/_internal/compiler/js_lib/js_names.dart
@@ -80,14 +80,7 @@ Map<String, String> computeReflectiveNames(Map<String, String> map) {
 
 @NoInline()
 List extractKeys(victim) {
-  var result = JS('', '''
-(function(victim, hasOwnProperty) {
-  var result = [];
-  for (var key in victim) {
-    if (hasOwnProperty.call(victim, key)) result.push(key);
-  }
-  return result;
-})(#, Object.prototype.hasOwnProperty)''', victim);
+  var result = JS('', 'Object.keys(#)', victim);
   return new JSArray.markFixed(result);
 }