Correctly handlify Dictionary::CollectKeysTo.

Correctly handlify Dictionary::CollectKeysTo.

'this' is a raw pointer and can be invalidated through GC, even
though the rest of the code is correctly handlified.

R=cbruni@chromium.org, jkummerow@chromium.org
BUG=v8:4570
LOG=N

Committed: https://crrev.com/912314be27451acf79106b35d3d09f6565c913cc
Cr-Commit-Position: refs/heads/master@{#32208}

[Yang, 2015-11-24 13:19:43]

The CQ bit was checked by yangguo@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-11-24 13:19:46]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1475633002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1475633002/1

[Jakob Kummerow, 2015-11-24 13:23:08]

lgtm

[commit-bot: I haz the power, 2015-11-24 13:40:26]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-11-24 13:40:26]

Dry run: This issue passed the CQ dry run.

[Yang, 2015-11-24 13:40:42]

The CQ bit was checked by yangguo@chromium.org

[commit-bot: I haz the power, 2015-11-24 13:40:57]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1475633002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1475633002/1

[commit-bot: I haz the power, 2015-11-24 13:43:28]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-11-24 13:44:05]

Patchset 1 (id:??) landed as
https://crrev.com/912314be27451acf79106b35d3d09f6565c913cc
Cr-Commit-Position: refs/heads/master@{#32208}