Reland of base: Make shared memory backed by Mach primitives by default.

Reland of base: Make shared memory backed by Mach primitives by default. (patchset #1 id:1 of https://codereview.chromium.org/1472313002/ )

Reason for revert:
Relanding. Looks like the failures may have been unrelated after all.

Original issue's description:
> Revert of base: Make shared memory backed by Mach primitives by default. (patchset #3 id:40001 of https://codereview.chromium.org/1453383002/ )
>
> Reason for revert:
> Speculative revert: 3 mac perf bots started timing out in random tests around the time this patch landed. I'll keep an eye on the waterfall and reland if things don't improve.
>
> See https://code.google.com/p/chromium/issues/detail?id=561416 for logs.
>
> Original issue's description:
> > base: Make shared memory backed by Mach primitives by default.
> >
> > The type of shared memory used is controlled by an A/B experiment. If the
> > experiment isn't present, use Mach primitives.
> >
> > BUG=466437
> >
> > Committed: https://crrev.com/8b8e4212cef52b2cf924c27bb7c49e375306acb3
> > Cr-Commit-Position: refs/heads/master@{#361249}
>
> TBR=mark@chromium.org,avi@chromium.org,erikchen@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=466437
>
> Committed: https://crrev.com/3e6b742e634e657d87c3267c2a8f9158c297f801
> Cr-Commit-Position: refs/heads/master@{#361630}

TBR=mark@chromium.org,avi@chromium.org,erikchen@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=466437
Committed: https://crrev.com/8e53d1be210193655b682ab381c3377700705067
Cr-Commit-Position: refs/heads/master@{#361869}

[Sami, 2015-11-26 11:41:32]

Created Reland of base: Make shared memory backed by Mach primitives by default.

[commit-bot: I haz the power, 2015-11-26 11:41:55]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1474073002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1474073002/1

[commit-bot: I haz the power, 2015-11-26 11:42:42]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-11-26 11:43:37]

Description was changed from

==========
Reland of base: Make shared memory backed by Mach primitives by default.
(patchset #1 id:1 of https://codereview.chromium.org/1472313002/ )

Reason for revert:
Relanding. Looks like the failures may have been unrelated after all.

Original issue's description:
> Revert of base: Make shared memory backed by Mach primitives by default.
(patchset #3 id:40001 of https://codereview.chromium.org/1453383002/ )
> 
> Reason for revert:
> Speculative revert: 3 mac perf bots started timing out in random tests around
the time this patch landed. I'll keep an eye on the waterfall and reland if
things don't improve.
> 
> See https://code.google.com/p/chromium/issues/detail?id=561416 for logs.
> 
> Original issue's description:
> > base: Make shared memory backed by Mach primitives by default.
> >
> > The type of shared memory used is controlled by an A/B experiment. If the
> > experiment isn't present, use Mach primitives.
> >
> > BUG=466437
> >
> > Committed: https://crrev.com/8b8e4212cef52b2cf924c27bb7c49e375306acb3
> > Cr-Commit-Position: refs/heads/master@{#361249}
> 
> TBR=mark@chromium.org,avi@chromium.org,erikchen@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=466437
> 
> Committed: https://crrev.com/3e6b742e634e657d87c3267c2a8f9158c297f801
> Cr-Commit-Position: refs/heads/master@{#361630}

TBR=mark@chromium.org,avi@chromium.org,erikchen@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=466437
==========

to

==========
Reland of base: Make shared memory backed by Mach primitives by default.
(patchset #1 id:1 of https://codereview.chromium.org/1472313002/ )

Reason for revert:
Relanding. Looks like the failures may have been unrelated after all.

Original issue's description:
> Revert of base: Make shared memory backed by Mach primitives by default.
(patchset #3 id:40001 of https://codereview.chromium.org/1453383002/ )
>
> Reason for revert:
> Speculative revert: 3 mac perf bots started timing out in random tests around
the time this patch landed. I'll keep an eye on the waterfall and reland if
things don't improve.
>
> See https://code.google.com/p/chromium/issues/detail?id=561416 for logs.
>
> Original issue's description:
> > base: Make shared memory backed by Mach primitives by default.
> >
> > The type of shared memory used is controlled by an A/B experiment. If the
> > experiment isn't present, use Mach primitives.
> >
> > BUG=466437
> >
> > Committed: https://crrev.com/8b8e4212cef52b2cf924c27bb7c49e375306acb3
> > Cr-Commit-Position: refs/heads/master@{#361249}
>
> TBR=mark@chromium.org,avi@chromium.org,erikchen@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=466437
>
> Committed: https://crrev.com/3e6b742e634e657d87c3267c2a8f9158c297f801
> Cr-Commit-Position: refs/heads/master@{#361630}

TBR=mark@chromium.org,avi@chromium.org,erikchen@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=466437

Committed: https://crrev.com/8e53d1be210193655b682ab381c3377700705067
Cr-Commit-Position: refs/heads/master@{#361869}
==========

[commit-bot: I haz the power, 2015-11-26 11:43:37]

Patchset 1 (id:??) landed as
https://crrev.com/8e53d1be210193655b682ab381c3377700705067
Cr-Commit-Position: refs/heads/master@{#361869}