chromeos: Add vm-launching bits for betty tests.

This duplicates the conditional in DEPS. We can't merge the two since:

- We want bots to do all their downloady bits in bot_update/runhooks.

- Some devs are likely used to using the simplechrome sdk without an
appropriate .gclient config setup. (The sdk will download all the things
everytime regardless of how you use it.)

So neither site (ie: DEPS & build/config/chromeos/rules.gni) can be the
single source of truth for the conditional :(

R=jbudorick

Bug: 947531
Change-Id: Ie50f483cf2ff06cad579dca2adae348e3c851f17
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1629711
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Commit-Queue: John Budorick <jbudorick@chromium.org>
Auto-Submit: Ben Pastene <bpastene@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#663363}
diff --git a/build/config/chromeos/rules.gni b/build/config/chromeos/rules.gni
index 0132d02..f4e5652 100644
--- a/build/config/chromeos/rules.gni
+++ b/build/config/chromeos/rules.gni
@@ -11,7 +11,7 @@
 declare_args() {
   # Determines if we're running tests on VMs or on devices.
   # TODO(crbug.com/866062): Is there a better way to do this?
-  cros_is_vm = cros_board == "amd64-generic"
+  cros_is_vm = cros_board == "amd64-generic" || cros_board == "betty"
 }
 
 # Ensure that if one is set, the other is as well.