GitLab

ShellPortMash is no longer always created. The code path this code
calls is only applicable to mash, so can early out for mus.

BUG=none
TEST=none

Change-Id: I55c58c353c0ebeba70cfec313a62c845e00faee9
Reviewed-on: https://chromium-review.googlesource.com/747204Reviewed-by: James Cook <jamescook@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512919}