This avoids the toolchain being wiped after using WinDbg.

Bug: None
Change-Id: I989ef7744b46254bab4c5a707724dc38a9b9a548
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2159998
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Scott Graham <scottmg@chromium.org>
Auto-Submit: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Scott Graham <scottmg@chromium.org>