Merge branch 'master' into master

Author: armanbilge

src/main/scala/org/scalajs/dom/raw/lib.scala

@@ -2566,6 +2566,8 @@ class Window
    */
   def close(): Unit = js.native
 
+  def closed: Boolean = js.native
+
   /**
    * The window.postMessage method safely enables cross-origin communication.
    * Normally, scripts on different pages are allowed to access each other if and only if