Bug 849723 - Introduce API to use the private hidden window correctly. r=ehsan

docshell/test/chrome/test_private_hidden_window.html

@@ -29,13 +29,7 @@ var mainWindow = window.QueryInterface(Ci.nsIInterfaceRequestor)
 // We need to wait for the hidden window to load, but can't access
 // an event target for a regular event listener.
 var hidden = mainWindow.Services.appShell.hiddenPrivateDOMWindow;
-var tmp = setTimeout(function poll() {
-  if (hidden.location.href != "resource://gre-resources/hiddenWindow.html" ||
-      !hidden.document.body) {
-    setTimeout(poll, 100);
-    return;
-  }
-
+mainWindow.PrivateBrowsingUtils.whenHiddenPrivateWindowReady(function(hidden) {
   var iframe = hidden.document.createElement('iframe');
   iframe.src = 'generic.html';
   hidden.document.body.appendChild(iframe);
@@ -46,7 +40,7 @@ var tmp = setTimeout(function poll() {
     win.close();
     win = null;
   }, false);
-}, 100);
+});
 
 function observer(aSubject, aTopic, aData) {
   is(aTopic, "last-pb-context-exited", "Unexpected observer topic");

toolkit/content/PrivateBrowsingUtils.jsm

@@ -42,6 +42,26 @@ this.PrivateBrowsingUtils = {
   },
   get isInTemporaryAutoStartMode() {
     return gTemporaryAutoStartMode;
+  },
+
+  whenHiddenPrivateWindowReady: function pbu_whenHiddenPrivateWindowReady(cb) {
+    Components.utils.import("resource://gre/modules/Timer.jsm", Timer);
+
+    let win = Services.appShell.hiddenPrivateDOMWindow;
+    function isNotLoaded() {
+      return ["complete", "interactive"].indexOf(win.document.readyState) == -1;
+    }
+    if (isNotLoaded()) {
+      setTimeout(function poll() {
+        if (isNotLoaded()) {
+          setTimeout(poll, 100);
+          return;
+        }
+        cb(Services.appShell.hiddenPrivateDOMWindow);
+      }, 4);
+    } else {
+      cb(Services.appShell.hiddenPrivateDOMWindow);
+    }
   }
 };