Bug 1244991: re-enable browser_backgroundTab.js UITour test and to make sure it doesn't fail on slower hardware, wait for the visibilitychange event explicitly since it may occur later than the tab open and switch. r=MattN

browser/components/uitour/test/browser.ini

@@ -6,7 +6,6 @@ support-files =
   ../UITour-lib.js
 
 [browser_backgroundTab.js]
-skip-if = e10s # Intermittent failures, bug 1244991
 [browser_closeTab.js]
 [browser_fxa.js]
 skip-if = debug || asan # updateAppMenuItem leaks

browser/components/uitour/test/browser_backgroundTab.js

@@ -7,7 +7,6 @@ var gContentWindow;
 requestLongerTimeout(2);
 add_task(setup_UITourTest);
 
-
 add_UITour_task(function* test_bg_getConfiguration() {
   info("getConfiguration is on the allowed list so should work");
   yield* loadForegroundTab();
@@ -20,7 +19,7 @@ add_UITour_task(function* test_bg_showInfo() {
   info("showInfo isn't on the allowed action list so should be denied");
   yield* loadForegroundTab();
 
-  yield showInfoPromise("appMenu", "Hello from the backgrund", "Surprise!").then(
+  yield showInfoPromise("appMenu", "Hello from the background", "Surprise!").then(
     () => ok(false, "panel shouldn't have shown from a background tab"),
     () => ok(true, "panel wasn't shown from a background tab"));
 
@@ -29,6 +28,19 @@ add_UITour_task(function* test_bg_showInfo() {
 
 
 function* loadForegroundTab() {
+  // Spawn a content task that resolves once we're sure the visibilityState was
+  // changed. This state is what the tests in this file rely on.
+  let promise = ContentTask.spawn(gBrowser.selectedTab.linkedBrowser, null, function* () {
+    return new Promise(resolve => {
+      let document = content.document;
+      document.addEventListener("visibilitychange", function onStateChange() {
+        Assert.equal(document.visibilityState, "hidden", "UITour page should be hidden now.");
+        document.removeEventListener("visibilitychange", onStateChange);
+        resolve();
+      });
+    });
+  });
   yield BrowserTestUtils.openNewForegroundTab(gBrowser);
+  yield promise;
   isnot(gBrowser.selectedTab, gTestTab, "Make sure tour tab isn't selected");
 }