[heap] Simplify zapping of old optimized code maps.

[heap] Simplify zapping of old optimized code maps.

This unconditionally enables zapping of old optimized code maps and
unifies the various zapping paths. The unconditional zapping, even if
heap verification is off, is needed because slots in the code map have
not been recorded and evacuation invariants break.

R=ulan@chromium.org

Committed: https://crrev.com/0c1994c64d5327cce706e7ae6bfec8da2ac4c7e4
Cr-Commit-Position: refs/heads/master@{#31895}

[ulan, 2015-11-09 17:14:51]

lgtm

[Michael Starzinger, 2015-11-09 17:18:03]

The CQ bit was checked by mstarzinger@chromium.org

[commit-bot: I haz the power, 2015-11-09 17:18:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1410833009/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1410833009/1

[commit-bot: I haz the power, 2015-11-09 17:19:50]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-11-09 17:20:13]

Patchset 1 (id:??) landed as
https://crrev.com/0c1994c64d5327cce706e7ae6bfec8da2ac4c7e4
Cr-Commit-Position: refs/heads/master@{#31895}