Try to fix a crash in the var tracking.

Try to fix a crash in the var tracking.

I think what is happening is that the list is mutated as we iterate over it.
This is actually quite a resonable thing to do: we're deleting objects, and
those objects may hold refs to other objects in our list.

BUG=http://crbug.com/133951

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=143644

[raymes, 2012-06-21 23:56:42]

lgtm

[commit-bot: I haz the power, 2012-06-22 00:40:57]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/brettw@chromium.org/10633019/1

[commit-bot: I haz the power, 2012-06-22 00:57:38]

Try job failure for 10633019-1 (retry) on mac_rel for step "compile" (clobber
build).
It's a second try, previously, step "compile" failed.
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=mac_rel&nu...

[commit-bot: I haz the power, 2012-06-22 16:57:22]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/brettw@chromium.org/10633019/5

[commit-bot: I haz the power, 2012-06-22 18:15:29]

Change committed as 143644