This adds a missing swarming config to the ubsan builders to fix
test isolation.

This also adds ubsan_vptr to the inferred options from build metadata.

For ubsan_vptr builds, the test runner makes sure to set up the
required options.

TBR=ishell@chromium.org

Bug: chromium:726584
Change-Id: I9667ba2b6d9d0f363f7cc94d23308e09da002d99
Reviewed-on: https://chromium-review.googlesource.com/577689Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46866}