Issue 6113 - Improve reliability of "block element" dialog

lib/filterComposer.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 220 matching lines @@
     else
       return browser.windows.get(window.id, {populate: true});
   }).then(window =>
   {
     let popupPageId = window.tabs[0].id;
 
     let doInitAttempt = 0;
     let doInit = () =>
     {
       doInitAttempt += 1;
       if (doInitAttempt > 30)

[kzar, 2017/12/07 13:28:33]

With other versions of Firefox e.g. 57 I found that sending every 100ms often
triggered the bug where sending seemed successful but with a response of
`undefined`, so I only retried every second in attempt to avoid that. With
Firefox 51 even that wasn't enough so I figured out this other approach. Since
we now have a way of detecting the problem I've switched back to 100ms again to
reduce the "Loading..." delay for the user.

         return;
 
       browser.tabs.sendMessage(popupPageId, {
         type: "composer.dialog.init",
         sender: sender.page.id,
         filters: message.filters
       }).then(response =>
       {
         // Sometimes sendMessage incorrectly reports a success on Firefox, so
         // we must check the response too.
-        if (typeof response == "undefined")

[Wladimir Palant, 2017/12/12 12:14:52]

Nit: why not `if (!response)`?

[kzar, 2017/12/12 12:33:14]

Done.

+        if (!response)
           throw new Error();
       }).catch(e =>
       {
         // Firefox sometimes sets the status for a window to "complete" before
         // it is ready to receive messages[1]. As a workaround we'll try again a
         // few times with a second delay.
         // [1] - https://bugzilla.mozilla.org/show_bug.cgi?id=1418655
         setTimeout(doInit, 100);
       });
     };
@@ skipping 55 matching lines @@
 {
   return quoteCSS(message.CSS);
 });
 
 ext.pages.onLoading.addListener(page =>
 {
   // A newly opened tab that is still loading has its URL set to about:blank
   if (/^https?:/.test(page.url.protocol))
     page.sendMessage({type: "composer.content.finished"});
 });