This will be used by various things in build and build_internal which
"need" a depot_tools on PATH (though I suspect most of those should be
refactored to use the depot_tools in chromium/src.git).

R=tandrii@chromium.org

Bug: 789808
Change-Id: I5d0590ccdc5482bd8e3048ad46a39b5aedacbddb
Reviewed-on: https://chromium-review.googlesource.com/828465Reviewed-by: Vadim Shtayura <vadimsh@chromium.org>
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Commit-Queue: Robbie Iannucci <iannucci@chromium.org>