bindings: Fixes connect-helper to use stringifyDOMObject.

LayoutTests/http/tests/navigatorconnect/resources/connect-helper.js

+try {
+  importScripts("/js-test-resources/js-test.js");

[jsbell, 2015/01/30 17:58:10]

Can we do this instead:

if ('importScripts' in self)
  importScripts(...);

Or at least add comment inside the try block e.g. "in case we're running in a
worker"

[Yuki, 2015/02/02 07:51:12]

Done.

+} catch (e) {}
+
 self.onmessage = function(e) {
   navigator.connect(e.data.connect)
     .then(function(port) {
         e.data.port.postMessage({success: true, result: port}, [port]);
       })
     .catch(function(error) {
         // Not all errors can be serialized as a SerializedScriptValue, so
         // convert to JSON and parse to get just the bits that certainly can.
         e.data.port.postMessage(
-          {success: false, result: JSON.parse(JSON.stringify(error))});
+          {success: false, result: JSON.parse(stringifyDOMObject(error))});
       });
 };