Stop JSON-encoding cross-frame messages.

lib/src/runner/browser/post_message_channel.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:convert';
 import 'dart:html';
 
 import 'package:stream_channel/stream_channel.dart';
 
 /// Constructs a [StreamChannel] wrapping `postMessage` communication with the
 /// host page.
 StreamChannel postMessageChannel() {
   var controller = new StreamChannelController(sync: true);
 
   window.onMessage.listen((message) {
     // A message on the Window can theoretically come from any website. It's
     // very unlikely that a malicious site would care about hacking someone's
     // unit tests, let alone be able to find the test server while it's
     // running, but it's good practice to check the origin anyway.
     if (message.origin != window.location.origin) return;
     message.stopPropagation();
 
-    // See host.dart for why we have to explicitly decode here.
-    controller.local.sink.add(JSON.decode(message.data));
+    controller.local.sink.add(message.data);
   });
 
   controller.local.stream.listen((data) {
     // TODO(nweiz): Stop manually adding href here once issue 22554 is
     // fixed.
     window.parent.postMessage({
       "href": window.location.href,
       "data": data
     }, window.location.origin);
   });
 
   // Send a ready message once we're listening so the host knows it's safe to
   // start sending events.
   window.parent.postMessage({
     "href": window.location.href,
     "ready": true
   }, window.location.origin);
 
   return controller.foreign;
 }