Add layout tests that test connecting to a system supplied navigator.connect service.

LayoutTests/http/tests/navigatorconnect/resources/test-helpers.js

 // Helper method that waits for a {success: <boolean>, result: any} reply on
 // a port and returns a promise that resolves (if success is true) or rejects
 // the promise with the value of the result attribute.
 function reply_as_promise(t, port) {
   return new Promise(function(resolve, reject) {
       var got_reply = false;
       port.onmessage = t.step_func(function(event) {
         assert_false(got_reply);
         assert_true('success' in event.data);
         assert_true('result' in event.data);
         got_reply = true;
         if (event.data.success)
           resolve(event.data.result);
         else
           reject(event.data.result);
       });
     });
 }
 
 // Method that behaves similarly to navigator.connect, but the actual connect
 // call is made from a cross origin iframe.
 function cross_origin_connect(t, service) {
-  // |service| is a relative URL, but for this to work from the iframe it needs
-  // an absolute URL.
-  var target_url = location.origin + base_path() + service;
+  // |service| could be a relative URL, but for this to work from the iframe it
+  // needs an absolute URL.
+  var target_url = new URL(service, location.origin + base_path());
   return with_iframe(
       cross_origin + base_path() + 'resources/connect-helper.html')
     .then(function(iframe) {
         var channel = new MessageChannel();
         iframe.contentWindow.postMessage(
-          {connect: target_url, port: channel.port2}, '*', [channel.port2]);
+          {connect: target_url.href, port: channel.port2}, '*', [channel.port2]);
         return reply_as_promise(t, channel.port1);
     });
 }
 
 // Method that behaves similarly to navigator.connect, but the actual connect
 // call is made from a worker.
 function connect_from_worker(t, service) {
   // |service| is a relative URL, but for this to work from the worker it needs
   // an absolute URL.
   var target_url = location.origin + base_path() + service;
   var worker = new Worker('resources/connect-helper.js');
   var channel = new MessageChannel();
   worker.postMessage
     ({connect: target_url, port: channel.port2}, [channel.port2]);
   return reply_as_promise(t, channel.port1);
 }