Issue 6496 - Account for browsers that don't support notifications with buttons

lib/notificationHelper.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 188 matching lines @@
       let notificationOptions = {
         type: "basic",
         title,
         iconUrl,
         message,
         buttons: activeButtons.map(button => ({title: button.title})),
         // We use the highest priority to prevent the notification
         // from closing automatically.
         priority: 2
       };
-      browser.notifications.create("", notificationOptions, () =>
+
+      // Firefox and Opera don't support buttons. Firefox throws synchronously,
+      // while Opera gives an asynchronous error. Wrapping the promise like
+      // this, turns the synchronus error on Firefox into a promise rejection.

[kzar, 2018/03/19 08:34:59]

Nit: Spelling of "synchronous"

[Sebastian Noack, 2018/03/19 16:58:23]

Done.

+      new Promise(resolve =>
       {
-        // Opera does not support the addition of buttons to notifications.
-        // Question type notfications always include buttons.
-        if (browser.runtime.lastError && activeNotification.type != "question")
+        resolve(browser.notifications.create(notificationOptions));
+      }).catch(() =>
+      {
+        // Without buttons, showing notifications of the type "question" is
+        // pointless. For other notifications, retry with the buttons removed.
+        if (activeNotification.type != "question")
         {
           delete notificationOptions.buttons;
-          browser.notifications.create("", notificationOptions);
+          browser.notifications.create(notificationOptions);
         }
       });
     }
     else if ("Notification" in window && activeNotification.type != "question")
     {
       if (linkCount > 0)
       {
         message += " " + browser.i18n.getMessage(
           "notification_without_buttons"
         );
@@ skipping 66 matching lines @@
   let methods = displayMethods[notificationType] || defaultDisplayMethods;
   return methods.includes(method);
 };
 
 ext.pages.onLoading.addListener(page =>
 {
   NotificationStorage.showNext(stringifyURL(page.url));
 });
 
 NotificationStorage.addShowListener(showNotification);