d8 workers: fix race on quit() with context_mutex_

test/mjsunit/regress/regress-4279.js

Index: test/mjsunit/regress/regress-4279.js
diff --git a/test/mjsunit/regress/regress-crbug-501711.js b/test/mjsunit/regress/regress-4279.js
similarity index 64%
copy from test/mjsunit/regress/regress-crbug-501711.js
copy to test/mjsunit/regress/regress-4279.js
index f8eda6e8d8e26f41b79e05af891b0f5446b5cd37..64ef967d8941cf384125b7bfbe2a04dd88fddd59 100644
--- a/test/mjsunit/regress/regress-crbug-501711.js
+++ b/test/mjsunit/regress/regress-4279.js
@@ -2,13 +2,10 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --stack-size=100
-
-function f() {
+if (this.Worker && this.quit) {
   try {
-    f();
-  } catch(e) {
-    Realm.create();
-  }
+      new Function(new Worker("55"));
+  } catch(err) {}
+
+  quit();
 }
-f();