repo: auto-update depot_tools when used

Since gclient automatically syncs this checkout when used,
have repo do the same for CrOS users.

Bug: 1148984
Test: ran and saw it auto-update when used externally
Test: ran and saw it not auto-update when used inside of a repo checkout
Change-Id: I56b9a45ef3a9ed501f6277e8f8357d4719cf2557
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2537164
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Michael Mortensen <mmortensen@google.com>
Commit-Queue: Mike Frysinger <vapier@chromium.org>

OWNERS

@@ -22,6 +22,7 @@ per-file chrome_set_ver=file://CROS_OWNERS
 per-file cros=file://CROS_OWNERS
 per-file cros_sdk=file://CROS_OWNERS
 per-file repo=file://CROS_OWNERS
+per-file repo_launcher=file://CROS_OWNERS
 per-file CROS_OWNERS=file://CROS_OWNERS
 
 # for the Goma client update