MessageEvent constructor should accept a MessagePort as source

LayoutTests/fast/events/constructors/message-event-constructor.html

Index: LayoutTests/fast/events/constructors/message-event-constructor.html
diff --git a/LayoutTests/fast/events/constructors/message-event-constructor.html b/LayoutTests/fast/events/constructors/message-event-constructor.html
index 4e6e5ee4dcd1f3376a98c270029ad72080334c44..c23fbe3fd82bc17f12030874f7e26d6d380fb188 100644
--- a/LayoutTests/fast/events/constructors/message-event-constructor.html
+++ b/LayoutTests/fast/events/constructors/message-event-constructor.html
@@ -73,9 +73,9 @@ shouldBe("new MessageEvent('eventType', { source: this }).source", "this");
 
 // MessagePort objects.
 var channel = new MessageChannel();
-shouldBe("new MessageEvent('eventType', { ports: [channel.port1], source: channel.port1 }).source", "null");
+shouldBe("new MessageEvent('eventType', { ports: [channel.port1], source: channel.port1 }).source", "channel.port1");
 
-// Non-window objects.
+// Unacceptable source objects (not a Window or a MessagePort).
 shouldBe("new MessageEvent('eventType', { source: test_object }).source", "null");
 shouldBe("new MessageEvent('eventType', { source: document }).source", "null");
 shouldBe("new MessageEvent('eventType', { source: document.body }).source", "null");