Added window extensions

Author: FlorianRappl

src/AngleSharp.Js/Dom/WindowExtensions.cs

@@ -0,0 +1,34 @@
+namespace AngleSharp.Js.Dom
+{
+    using AngleSharp.Attributes;
+    using AngleSharp.Browser;
+    using AngleSharp.Dom;
+    using AngleSharp.Dom.Events;
+    using System;
+
+    /// <summary>
+    /// Defines a set of extensions for the window object.
+    /// </summary>
+    [DomExposed("Window")]
+    public static class WindowExtensions
+    {
+        /// <summary>
+        /// Posts a message.
+        /// </summary>
+        [DomName("postMessage")]
+        public static void PostMessage(this IWindow window, String message, String targetOrigin = "*", Object transfer = null)
+        {
+            var ev = new MessageEvent("message", false, false, message, targetOrigin);
+            var document = window.Document;
+            var loop = document.Context.GetService<IEventLoop>();
+            loop.EnqueueAsync(_ => window.Fire(ev));
+        }
+
+        /// <summary>
+        /// Gets the top window context.
+        /// </summary>
+        [DomName("top")]
+        [DomAccessor(Accessors.Getter)]
+        public static IWindow Top(this IWindow window) => window.Document.Context?.Creator?.DefaultView;
+    }
+}