override: intialise BrowserWindowProxy.closed

atom/renderer/lib/override.coffee

@@ -11,6 +11,7 @@ resolveUrl = (url) ->
 # Window object returned by "window.open".
 class BrowserWindowProxy
   constructor: (@guestId) ->
+    @closed = false
     ipc.on 'ATOM_SHELL_GUEST_WINDOW_MANAGER_WINDOW_CLOSED', (guestId) =>
       if guestId is @guestId
         @closed = true

spec/chromium-spec.coffee

@@ -37,6 +37,7 @@ describe 'chromium feature', ->
   describe 'window.open', ->
     it 'returns a BrowserWindowProxy object', ->
       b = window.open 'about:blank', 'test', 'show=no'
+      assert.equal b.closed, false
       assert.equal b.constructor.name, 'BrowserWindowProxy'
       b.close()