Add CHECKs when updating pointers from the slots and store buffers

Add CHECKs  when updating pointers from the slots and store buffers

We want to verify that we always overwrite heap objects with heap
objects, and non-heap objects with non-heap objects

BUG=chromium:452095
R=hpayer@chromium.org
LOG=n

Committed: https://crrev.com/58fbcfac8ae82b1241f07e1b8ea81a5973514c11
Cr-Commit-Position: refs/heads/master@{#27479}

[jochen (gone - plz use gerrit), 2015-03-25 16:37:43]

ptal

[jochen (gone - plz use gerrit), 2015-03-26 11:00:26]

ptal - added comments

[Hannes Payer (out of office), 2015-03-26 11:42:11]

This CL may have performance impact. Let's check the performance bots after
landing. LGTM

[jochen (gone - plz use gerrit), 2015-03-26 13:28:22]

The CQ bit was checked by jochen@chromium.org

[commit-bot: I haz the power, 2015-03-26 13:28:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1035763002/40001

[jochen (gone - plz use gerrit), 2015-03-26 13:29:03]

i guess we can revert it after one dev channel release - either we find a
smoking gun, or if not, my theory is wrong

[commit-bot: I haz the power, 2015-03-26 13:29:31]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-03-26 13:29:52]

Patchset 3 (id:??) landed as
https://crrev.com/58fbcfac8ae82b1241f07e1b8ea81a5973514c11
Cr-Commit-Position: refs/heads/master@{#27479}

[jochen (gone - plz use gerrit), 2015-04-01 14:35:17]

A revert of this CL (patchset #3 id:40001) has been created in
https://codereview.chromium.org/1052713002/ by jochen@chromium.org.

The reason for reverting is: Got one dev-channel with this. Should be enough..