Issue 6385 - Don't attempt to inject styles for frames we can't find

lib/cssInjection.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 89 matching lines @@
 }
 
 function updateFrameStyles(tabId, frameId, selectors, groupName)
 {
   let styleSheet = null;
   if (selectors.length > 0)
     styleSheet = createStyleSheet(selectors);
 
   let frame = ext.getFrame(tabId, frameId);
   if (!frame)
-    return;

[Manish Jethani, 2018/02/14 13:41:16]

OK, I guess this is the right thing to do. But we should return false
explicitly.

[Manish Jethani, 2018/02/14 14:03:41]

If this is reproduceable, we should check why it is happening. Clearly the
content script is still around when it gets a response, then we should find out
why ext.getFrame doesn't find the frame.

[kzar, 2018/02/14 14:52:58]

This is reproducible, the issue description is up to date with steps of how to
reproduce and also my findings (tl;dr `framesOfTabs` really doesn't have the
frame in question - I'm not sure why).

[kzar, 2018/02/14 14:52:58]

Done.

[Manish Jethani, 2018/02/15 14:06:22]

See my comment here:

https://issues.adblockplus.org/ticket/6385#comment:3

So I think this is OK as a short-term fix, but I think this is going to happen
very often on Firefox so we should try to do something better.

LGTM

+    return false;
 
   if (!frame.injectedStyleSheets)
     frame.injectedStyleSheets = new Map();
 
   let oldStyleSheet = frame.injectedStyleSheets.get(groupName);
 
   // Ideally we would compare the old and new style sheets and skip this code
   // if they're the same, but the old style sheet can be a leftover from a
   // previous instance of the frame. We must add the new style sheet
   // regardless.
@@ skipping 55 matching lines @@
     response.inlineEmulated = true;
 
   return response;
 });
 
 port.on("elemhide.injectSelectors", (message, sender) =>
 {
   updateFrameStyles(sender.page.id, sender.frame.id, message.selectors,
                     message.groupName);
 });