[d8] remove utility context.

src/d8.js

Index: src/d8.js
diff --git a/src/d8.js b/src/d8.js
index 27a0bc39cd07107cb03fa65f0c12534aed45573a..e49c6b74580637c6da18b26d72d4fd34ea8f59cf 100644
--- a/src/d8.js
+++ b/src/d8.js
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+(function() {
 "use strict";
 
 // A more universal stringify that supports more types than JSON.
@@ -89,3 +90,6 @@ function StringifyProxy(proxy, depth) {
   }
   return '[' + proxy_type + ' Proxy ' + Stringify(info_object, depth-1) + ']';
 }
+
+return Stringify;
+})();