Change GetGuestUserName() to kGuestUserName

Having a method that takes a string literal and returns a copy as
a std::string seems odd.  We can keep this as a kOnstant,
and reduce copies while also remaining more flexible.

CQ-DEPEND=I5aee09cb66e60ef3b5f8f64bf76d7dd7837dab41

BUG=None
TEST=build libchromeos

Change-Id: Ie070102429856f21e571cc1073e661d6b5b1c5f3
Reviewed-on: https://gerrit.chromium.org/gerrit/49605
Tested-by: Chris Masone <cmasone@chromium.org>
Reviewed-by: Will Drewry <wad@chromium.org>
Commit-Queue: Chris Masone <cmasone@chromium.org>
2 files changed