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

lib/cssInjection.js

Index: lib/cssInjection.js
diff --git a/lib/cssInjection.js b/lib/cssInjection.js
index e5a918d54c1eef5e016a7fc80b729ce31328ebe3..acf6274d7340a14cc8626018036923c5371cd3b2 100644
--- a/lib/cssInjection.js
+++ b/lib/cssInjection.js
@@ -106,6 +106,9 @@ function updateFrameStyles(tabId, frameId, selectors, groupName)
     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

+
   if (!frame.injectedStyleSheets)
     frame.injectedStyleSheets = new Map();