gclient validate: allow "recursion" setting
gclient validate: allow "recursion" setting

It's still used in some places like CDM.

This fixes the bug below.

Bug: 728343
Change-Id: I0f9e2bbd0339838ee6d1d240c584858947cf36d2
Reviewed-on: https://chromium-review.googlesource.com/522682
Commit-Queue: Paweł Hajdan Jr. <84cab74a96a175cf90ed68b8abab420352923e11@chromium.org>
Reviewed-by: Emma Soederberg <586d02eb8c8839ff15280b17dbcdb389ac64f4fb@google.com>

CoherentLabs/depot_tools,CoherentLabs/depot_tools