fix: add disable-renderer-backgrounding flag

[cexbrayat]

Fixes #123

[rogeriopvl]

@cexbrayat thanks for the PR.

From what I understand, it should be enough to just use the --disable-background-timer-throttling flag, but on OSX it's not and it needs the --disable-renderer-backgrounding to completely disable that behaviour. Is it correct? If it is, then we need a comment documenting this work around.

I've been able to run a test suite with this flag and can confirm that there are performance gains that justify merging this.

[cexbrayat]

@rogeriopvl Thank you for considering this. You're correct, this only improves performance on OSX (https://bugs.chromium.org/p/chromium/issues/detail?id=605498#c1 is probably the Chrome related issue).

I added a comment to document the workaround, let me know if that's enough.

[rogeriopvl]

@cexbrayat looks good 👍

[rogeriopvl]

@dignifiedquire we should do a patch release

[dignifiedquire]

done