Fix prototype registration upon SlowToFast migration

Fix prototype registration upon SlowToFast migration

When a prototype object migrates from a slow to a fast map, where the slow map
was registered as a user of its own prototype, then the registration must be
transferred to the new map (just like MigrateToMap does for all other cases).

BUG=chromium:513602
LOG=y
NOTREECHECKS=true

Committed: https://crrev.com/c906efd5d18dba6e391fc536a594a50885c13f49
Cr-Commit-Position: refs/heads/master@{#29898}

[Jakob Kummerow, 2015-07-28 15:14:19]

jkummerow@chromium.org changed reviewers:
+ ulan@chromium.org

[Jakob Kummerow, 2015-07-28 15:14:19]

PTAL.

https://codereview.chromium.org/1263543004/diff/1/src/objects.cc
File src/objects.cc (right):

https://codereview.chromium.org/1263543004/diff/1/src/objects.cc#newcode4659
src/objects.cc:4659: if (maybe_old_prototype->IsJSObject()) {
This if-block is new; the other changes are just refactoring.

[ulan, 2015-07-28 15:18:32]

lgtm

[Jakob Kummerow, 2015-07-28 15:19:27]

The CQ bit was checked by jkummerow@chromium.org

[commit-bot: I haz the power, 2015-07-28 15:19:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1263543004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1263543004/1

[commit-bot: I haz the power, 2015-07-28 15:41:26]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-07-28 15:41:40]

Patchset 1 (id:??) landed as
https://crrev.com/c906efd5d18dba6e391fc536a594a50885c13f49
Cr-Commit-Position: refs/heads/master@{#29898}