[Mac] Shut down connections to WindowServer before engaging the sandbox.

This is only done for Mac OS versions 10.8 and higher.

A similar CL was landed and reverted:
https://chromium.googlesource.com/chromium/src.git/+/cef0cb9e60fb0f47562be83f8aa117899f0314d5

BUG=397642, 306348
TEST=Manually tested on 10.6-10.10.
R=avi@chromium.org, jeremy@chromium.org

Review URL: https://codereview.chromium.org/673443002

Cr-Commit-Position: refs/heads/master@{#300891}
1 file changed