[turbofan] Finish support for holey double elements backing stores.

[turbofan] Finish support for holey double elements backing stores.

Also properly support loading from holey double element backing stores
in JSNativeContextSpecialization. This adds a new simplified operator
NumberIsHoleNaN, which checks whether a certain value is the special NaN
that we use to encode "the hole" in holey double element backing stores.

R=jarin@chromium.org
BUG=v8:4470
LOG=n

Committed: https://crrev.com/5716426b26e933b85b6bf0fd4f2fd94a8b51ce24
Cr-Commit-Position: refs/heads/master@{#32039}

[Benedikt Meurer, 2015-11-17 12:04:35]

Hey Jaro,

Finishing series of patches for native context specialization.
Next is refactoring round 1 :-)
Please take a look.

Thanks,
Benedikt

[Jarin, 2015-11-17 12:34:51]

lgtm

[Benedikt Meurer, 2015-11-17 13:04:51]

The CQ bit was checked by bmeurer@chromium.org

[commit-bot: I haz the power, 2015-11-17 13:05:01]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1448343002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1448343002/1

[commit-bot: I haz the power, 2015-11-17 13:14:15]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-11-17 13:14:30]

Patchset 1 (id:??) landed as
https://crrev.com/5716426b26e933b85b6bf0fd4f2fd94a8b51ce24
Cr-Commit-Position: refs/heads/master@{#32039}