Allow IdentityMap to store Smi-0.

Allow IdentityMap to store Smi-0.

R=bmeurer@chromium.org

Committed: https://crrev.com/f430bd040f5d518cbbc9cdfffa362bb108f18cf2
Cr-Commit-Position: refs/heads/master@{#31470}

[Yang, 2015-10-22 11:34:43]

I created a symbol as sentinel for empty hash table entries. In theory, any
address that does not collide with a smi or a heap object that we want to use as
key in the IdentityMap would work. For example 0x1 or 0xffffffff. But this looks
safer and cleaner :)

[Benedikt Meurer, 2015-10-22 11:35:13]

Awesome! LGTM

[Benedikt Meurer, 2015-10-22 11:36:20]

The CQ bit was checked by bmeurer@chromium.org

[commit-bot: I haz the power, 2015-10-22 11:36:29]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1417203003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1417203003/1

[commit-bot: I haz the power, 2015-10-22 11:39:07]

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

[commit-bot: I haz the power, 2015-10-22 11:39:08]

Try jobs failed on following builders:
  v8_presubmit on tryserver.v8 (JOB_FAILED,
http://build.chromium.org/p/tryserver.v8/builders/v8_presubmit/builds/6938)

[Yang, 2015-10-22 11:51:22]

yangguo@chromium.org changed reviewers:
+ hpayer@chromium.org

[Yang, 2015-10-22 11:51:23]

Hannes, please take a look at the heap changes, thanks.

[Hannes Payer (out of office), 2015-10-22 11:51:53]

heap LGTM

[Yang, 2015-10-22 12:10:38]

The CQ bit was checked by yangguo@chromium.org

[commit-bot: I haz the power, 2015-10-22 12:10:50]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1417203003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1417203003/1

[commit-bot: I haz the power, 2015-10-22 12:12:15]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-22 12:12:27]

Patchset 1 (id:??) landed as
https://crrev.com/f430bd040f5d518cbbc9cdfffa362bb108f18cf2
Cr-Commit-Position: refs/heads/master@{#31470}