With this, `git cl upload` will do the right thing for boringssl.

BUG=none
Change-Id: Icc83144ef39bc71c795c411e608e0b8c009f3a04
Reviewed-on: https://boringssl-review.googlesource.com/2331
Reviewed-by: David Benjamin <davidben@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>