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

test/mjsunit/regress/regress-crbug-505778.js

Index: test/mjsunit/regress/regress-crbug-505778.js
diff --git a/test/mjsunit/regress/regress-crbug-505778.js b/test/mjsunit/regress/regress-crbug-505778.js
index 9f14fd08002e6fccd5ee4266c0f63d07fe6926a0..74d96ab094295b9429b5bed7c2cc7268146b939b 100644
--- a/test/mjsunit/regress/regress-crbug-505778.js
+++ b/test/mjsunit/regress/regress-crbug-505778.js
@@ -3,9 +3,6 @@
 // found in the LICENSE file.
 
 if (this.Worker) {
-  function __f_3() {
-    onmessage = function() {}
-  }
-  var __v_7 = new Worker(__f_3);
+  var __v_7 = new Worker('onmessage = function() {}');
   __v_7.postMessage("");
 }