Stop JSON-encoding cross-frame messages.

lib/src/runner/browser/post_message_channel.dart

Index: lib/src/runner/browser/post_message_channel.dart
diff --git a/lib/src/runner/browser/post_message_channel.dart b/lib/src/runner/browser/post_message_channel.dart
index 865467536d6b77866d44d24dfe86c5e9adec3b95..f27ff6bce89f45a96d47491cf07a2611a23e16d9 100644
--- a/lib/src/runner/browser/post_message_channel.dart
+++ b/lib/src/runner/browser/post_message_channel.dart
@@ -20,8 +20,7 @@ StreamChannel postMessageChannel() {
     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) {