Split extra checks into extra checks and handle zapping

Split extra checks into extra checks and handle zapping

That will make it easier to turn on handle zapping alone and experiment
with it.

R=jkummerow@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=17004

[Jakob Kummerow, 2013-09-30 11:39:23]

lgtm

[jochen (gone - plz use gerrit), 2013-09-30 11:57:05]

Committed patchset #1 manually as r17004 (presubmit successful).