Support asynchronous main methods.

lib/src/runner/browser/iframe_listener.dart

Index: lib/src/runner/browser/iframe_listener.dart
diff --git a/lib/src/runner/browser/iframe_listener.dart b/lib/src/runner/browser/iframe_listener.dart
index b345f3795adecb5bf59702faa12c4f8367b11281..76804517adbcb9adf3422e950dd0b608cd1cfa91 100644
--- a/lib/src/runner/browser/iframe_listener.dart
+++ b/lib/src/runner/browser/iframe_listener.dart
@@ -56,24 +56,23 @@ class IframeListener {
     }
 
     var declarer = new Declarer();
-    try {
-      runZoned(main, zoneValues: {#test.declarer: declarer});
-    } catch (error, stackTrace) {
+    runZoned(() => new Future.sync(main), zoneValues: {
+      #test.declarer: declarer
+    }).then((_) {
+      var url = Uri.parse(window.location.href);
+      var message = JSON.decode(Uri.decodeFull(url.fragment));
+      var metadata = new Metadata.deserialize(message['metadata']);
+      var browser = TestPlatform.find(message['browser']);
+
+      var suite = new Suite(declarer.tests, metadata: metadata)
+          .forPlatform(browser);
+      new IframeListener._(suite)._listen(channel);
+    }, onError: (error, stackTrace) {
       channel.sink.add({
         "type": "error",
         "error": RemoteException.serialize(error, stackTrace)
       });
-      return;
-    }
-
-    var url = Uri.parse(window.location.href);
-    var message = JSON.decode(Uri.decodeFull(url.fragment));
-    var metadata = new Metadata.deserialize(message['metadata']);
-    var browser = TestPlatform.find(message['browser']);
-
-    var suite = new Suite(declarer.tests, metadata: metadata)
-        .forPlatform(browser);
-    new IframeListener._(suite)._listen(channel);
+    });
   }
 
   /// Constructs a [MultiChannel] wrapping the `postMessage` communication with