PPC: [stubs] Optimize LoadGlobalViaContextStub and StoreGlobalViaContextStub.

PPC: [stubs] Optimize LoadGlobalViaContextStub and StoreGlobalViaContextStub.

Port d6ee366d5c5aef7c6bc550889a33520058b4e33a

Original commit message:
    This is the initial round of optimizations for the
    LoadGlobalViaContextStub and StoreGlobalViaContextStub, basically
    turning them into platform code stubs to avoid the Crankshaft overhead
    in the fast case, and making the runtime interface cheaper.

R=bmeurer@chromium.org, dstence@us.ibm.com, michael_dawson@ca.ibm.com
BUG=chromium:510694
LOG=n

Committed: https://crrev.com/4ad22295d41fd6f5cd40d8aa11c34c733c62fc30
Cr-Commit-Position: refs/heads/master@{#29867}

[dstence, 2015-07-24 21:06:49]

lgtm

[MTBrandyberry, 2015-07-24 21:09:50]

The CQ bit was checked by mbrandy@us.ibm.com

[commit-bot: I haz the power, 2015-07-24 21:09:58]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1261473002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1261473002/1

[commit-bot: I haz the power, 2015-07-24 21:16:01]

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

[commit-bot: I haz the power, 2015-07-24 21:16:01]

Try jobs failed on following builders:
  v8_presubmit on tryserver.v8 (JOB_FAILED,
http://build.chromium.org/p/tryserver.v8/builders/v8_presubmit/builds/4453)

[MTBrandyberry, 2015-07-24 21:33:13]

mbrandy@us.ibm.com changed reviewers:
+ danno@chromium.org

[MTBrandyberry, 2015-07-24 21:34:15]

On 2015/07/24 21:16:01, commit-bot: I haz the power wrote:
> Try jobs failed on following builders:
>   v8_presubmit on tryserver.v8 (JOB_FAILED,
> http://build.chromium.org/p/tryserver.v8/builders/v8_presubmit/builds/4453)

It appears that src/full-codegen/ppc is lacking an OWNERS file.  Can someone
else approve this while that gets sorted?

[Benedikt Meurer, 2015-07-27 10:50:31]

The CQ bit was checked by bmeurer@chromium.org

[Benedikt Meurer, 2015-07-27 10:50:31]

lgtm

[commit-bot: I haz the power, 2015-07-27 10:50:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1261473002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1261473002/1

[commit-bot: I haz the power, 2015-07-27 11:19:52]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-07-27 11:20:19]

Patchset 1 (id:??) landed as
https://crrev.com/4ad22295d41fd6f5cd40d8aa11c34c733c62fc30
Cr-Commit-Position: refs/heads/master@{#29867}