[turbofan] Split JSGlobalObjectSpecialization into separate class.

[turbofan] Split JSGlobalObjectSpecialization into separate class.

The JSNativeContextSpecialization class is getting rather huge with all
the stuff related to property and element access going in. Splitting off
the global object related stuff into JSGlobalObjectSpecialization seems
like a natural separation, especially since the global object
specialization is sort of separate issue anyway.  This is neutral
functionality- and performance-wise.

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

Committed: https://crrev.com/4eb41ba7385a594e7b17ce6a4f0ed4b039ccec8f
Cr-Commit-Position: refs/heads/master@{#31748}

[Benedikt Meurer, 2015-11-03 13:30:32]

Hey Jaro,

As mentioned before, I'm splitting the native context specialization into global
specialization and other native context specialization concerns.
Please take a look.

Thanks,
Benedikt

[Jarin, 2015-11-03 13:30:37]

lgtm

[Benedikt Meurer, 2015-11-03 13:30:48]

The CQ bit was checked by bmeurer@chromium.org

[commit-bot: I haz the power, 2015-11-03 13:30:55]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1417043006/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1417043006/1

[commit-bot: I haz the power, 2015-11-03 14:20:19]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-11-03 14:20:47]

Patchset 1 (id:??) landed as
https://crrev.com/4eb41ba7385a594e7b17ce6a4f0ed4b039ccec8f
Cr-Commit-Position: refs/heads/master@{#31748}