Disable some compositing state asserts seen on Mac builds

Disable some compositing state asserts seen on Mac builds

Test scenarios:
http://www.rbyers.net/eventTest.html - scrolling the page or div (has a wheel handler but doesn't call preventDefault)
Loading https://twitter.com/pwnall

BUG=343132
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=168478

[Rick Byers, 2014-03-04 21:34:26]

Ojan,
Please take a look.  I didn't dig into these in any detail to try to understand
them - just trying to unblock folks hitting these in development on Mac.

Thanks,
   Rick

[ojan, 2014-03-05 02:55:51]

lgtm

Would be nice to commit reduced versions of those pages along with this patch. I
worry that those pages will change and we'll lose the ability to reproduce this.
But I understand if you're too busy with other things.

[Rick Byers, 2014-03-05 02:57:41]

The CQ bit was checked by rbyers@chromium.org

[commit-bot: I haz the power, 2014-03-05 02:57:51]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/rbyers@chromium.org/180803012/1

[Rick Byers, 2014-03-05 03:25:03]

On 2014/03/05 02:55:51, ojan wrote:
> lgtm
> 
> Would be nice to commit reduced versions of those pages along with this patch.
I
> worry that those pages will change and we'll lose the ability to reproduce
this.
> But I understand if you're too busy with other things.

Thanks.  All but one of the asserts was for my rbyers.net/eventTest.html test
page which I don't change much.  It seems any page with a scrollable div and
wheel handler not consuming events is sufficient (forces a main-thread scroll
with scrollbars) - I'll post a simple reduction to the bug.

I spent ~10 min poking at the twitter case (the one remaining assert), but it
wasn't immediately obvious what the issue is.  It's certainly related to the
page having a background-attachment: fixed, but I can't get simple pages to
trigger it.  I can't afford to spend more time now, sorry.

[commit-bot: I haz the power, 2014-03-05 14:09:28]

Change committed as 168478