bisect-kit: fetch chrome repos parallelly

also consoliated comments why we need additional sync for chrome mirror

BUG=b:206567489
TEST=./setup_cros_bisect.py sync --chrome

Change-Id: I73c1ecae1c2bbe129d19bed20317bdd5bcffad2e
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/bisect-kit/+/3285523
Tested-by: Kuang-che Wu <kcwu@chromium.org>
Auto-Submit: Kuang-che Wu <kcwu@chromium.org>
Commit-Queue: Zheng-Jie Chang <zjchang@chromium.org>
Reviewed-by: Zheng-Jie Chang <zjchang@chromium.org>
1 file changed