[Mac] Enable the MacV2Sandbox in content_shell.

The main executable now invokes the SeatbeltExecServer when the feature
is enabled.

This also sets up the OuterBundle and BaseBundleID overrides, which are
required to properly find the rohitfork port.

Bug: 850735, 749839
Change-Id: Ic02df574a209213d1ca560ab2d1e947be5ae5136
Reviewed-on: https://chromium-review.googlesource.com/1099643
Reviewed-by: Greg Kerr <kerrnel@chromium.org>
Reviewed-by: Nasko Oskov <nasko@chromium.org>
Commit-Queue: Robert Sesek <rsesek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567496}
7 files changed