Bug 1458375 - Add browser-idle-startup-tasks-finished notification to Fennec. r=snorp

MozReview-Commit-ID: CDEMUCL8ykG

--HG--
extra : rebase_source : 5655f7eb3fb5092c202fde41967b23323162baaf

mobile/android/chrome/content/browser.js

@@ -554,6 +554,12 @@ var BrowserApp = {
       // Bug 778855 - Perf regression if we do this here. To be addressed in bug 779008.
       InitLater(() => SafeBrowsing.init(), window, "SafeBrowsing");
 
+      // This should always go last, since the idle tasks (except for the ones with
+      // timeouts) should execute in order. Note that this observer notification is
+      // not guaranteed to fire, since the window could close before we get here.
+      InitLater(() => {
+        Services.obs.notifyObservers(window, "browser-idle-startup-tasks-finished");
+      });
     }, {once: true});
   },