GitLab

Added checkout_aemu to gclient_gn_args.
Check checkout_aemu when generating runner scripts, and only download
AEMU if the value is true.

Bug: b/142756812
Change-Id: Ic08b0abe945703ee5d6cddbc661831bbbdce784d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1879819
Commit-Queue: Chong Gu <chonggu@google.com>
Reviewed-by: Kevin Marshall <kmarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710117}