Fix ReferenceError of Worker in regress-crbug-503578

test/mjsunit/regress/regress-crbug-503578.js

Index: test/mjsunit/regress/regress-crbug-503578.js
diff --git a/test/mjsunit/regress/regress-crbug-503578.js b/test/mjsunit/regress/regress-crbug-503578.js
index 931509efebe57fb91427111b482b14a1f519173f..c32f8da06d7c5cec82e13ba93d5d3c0785525425 100644
--- a/test/mjsunit/regress/regress-crbug-503578.js
+++ b/test/mjsunit/regress/regress-crbug-503578.js
@@ -2,14 +2,16 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-function __f_1() {
-  onmessage = function() {}
+if (this.Worker) {
+  function __f_1() {
+    onmessage = function() {}
+  }
+  function __f_0(byteLength) {
+    var __v_1 = new ArrayBuffer(byteLength);
+    var __v_5 = new Uint32Array(__v_1);
+    return __v_5;
+  }
+  var __v_6 = new Worker(__f_1);
+  var __v_3 = __f_0(16);
+  __v_6.postMessage(__v_3);
 }
-function __f_0(byteLength) {
-  var __v_1 = new ArrayBuffer(byteLength);
-  var __v_5 = new Uint32Array(__v_1);
-  return __v_5;
-}
-var __v_6 = new Worker(__f_1);
-var __v_3 = __f_0(16);
-__v_6.postMessage(__v_3);