This tool will soon be added as a gclient hook for Mac developers to install the
requested Xcode version on their workstations, and it's easier if gclient can
assume it on PATH.

BUG=475693
R=iannucci@chromium.org

Change-Id: I6af90755bb2ee6de1e19e3a475d9a23bf75888c3
Reviewed-on: https://chromium-review.googlesource.com/756888Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: Aaron Gable <agable@chromium.org>
Commit-Queue: Sergey Berezin <sergeyberezin@chromium.org>