Change d8 Worker API so it takes a string instead of a function.

test/mjsunit/regress/regress-crbug-504136.js

Index: test/mjsunit/regress/regress-crbug-504136.js
diff --git a/test/mjsunit/regress/regress-crbug-504136.js b/test/mjsunit/regress/regress-crbug-504136.js
index 0061ebd91db014a9d171fcf547d537c7d7a5ef1d..4ed684354445ce2d4cc6cf9d1885b14ca8677cd6 100644
--- a/test/mjsunit/regress/regress-crbug-504136.js
+++ b/test/mjsunit/regress/regress-crbug-504136.js
@@ -3,8 +3,7 @@
 // found in the LICENSE file.
 
 if (this.Worker) {
-  function __f_5() {}
-  var __v_10 = new Worker(__f_5);
+  var __v_10 = new Worker('');
   __v_10.terminate();
  __v_10.getMessage();
 }