Revert of Turn off overapproximation of the weak closure again

Revert of Turn off overapproximation of the weak closure again (patchset #1 id:1 of https://codereview.chromium.org/1050443002/)

Reason for revert:
this indeed drops the max major gc time considerable, so turn it back on

Original issue's description:
> Turn off overapproximation of the weak closure again
>
> As long as we still have to process global handles, the impact is not
> yet worthwhile
>
> BUG=v8:3862
> R=hpayer@chromium.org
> LOG=y
>
> Committed: https://crrev.com/294cdc6aecbd7f76be68217da4b3d35901ebce4b
> Cr-Commit-Position: refs/heads/master@{#27570}

TBR=hpayer@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:3862
Committed: https://crrev.com/a7c1b0a92b603201dbb09547b935db5bb54a6e64
Cr-Commit-Position: refs/heads/master@{#27616}

[jochen (gone - plz use gerrit), 2015-04-07 09:45:20]

Created Revert of Turn off overapproximation of the weak closure again

[commit-bot: I haz the power, 2015-04-07 09:45:31]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1068723003/1

[commit-bot: I haz the power, 2015-04-07 09:46:02]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-07 09:46:20]

Patchset 1 (id:??) landed as
https://crrev.com/a7c1b0a92b603201dbb09547b935db5bb54a6e64
Cr-Commit-Position: refs/heads/master@{#27616}