Fixed set- and clearTimeout to make debugging working with Firefox

[keinhaar]

This fixes a problem that only occurs in firefox while debugging.
Without the fix SDBG Users would be forced to super-source the Impl class.
After a few weeks of testing i did'nt find any negative effects on runtime, or in other browsers.
Has been discussed in #9787.
Fixes #9787

[zbynek]

this PR is based on the patch that @niloc132 provided in the issue as a workaround with a comment

I don't think this is a reasonable fix to make to GWT itself, but it does look like we could remove the watchdog entirely, or only conditionally enable it.

so I think it would be better implement that instead.

[keinhaar]

so I think it would be better implement that instead.
Maybe, but nobody is working on removing the watchdog, and this is a very simple fix.
In all of my projects it works without any problems.
So i propose to do this now, and later on, somebody could remove the watchdog.

[niloc132]

Sorry for the delay on this. I finally simplified the bug report and filed it at https://bugzilla.mozilla.org/show_bug.cgi?id=1833637.

The watchdog timer isn't needed at all to see invalid behavior. Unfortunately, this shows that this patch doesn't go far enough - not only can the watchdog timer keep running, but any other timer can too - we have to fix any other call to $wnd.setTimeout to instead reference the local window/self, or we might hit other issues with this while a debugger is open. With the exception of RichTextAreaImplStandard and ScrollImpl, every call I see in GWT to setTimeout goes through $wnd, so will have this problem. Elemental2's DomGlobal.setTimeout will have this issue as well.

[keinhaar]

The same problem occurs in automated tests using selenium with the latest htmlunit-driver.
The proposed fix does resolve this too.

[niloc132]

That's interesting - did you file an issue with them showing the issue?

From the linked issue above, the underlying issue originally intended to be fixed by this patch is a regression in the FF debugger, with a workaround: In about:config, change devtools.every-frame-target.enabled to false. Note that changing GWT as this patch only fixes the bug for that specific timeout, but any other application code can still fail in this way, the best fix is to apply their workaround, since otherwise the bug can just come back another way.

[keinhaar]

I use the workaround in SDBG to avoid this problem.