The results are too noisy ATM. This switches off validate-asm for
default comparisons. We can add back dedicated jobs later that switch
it on.

BUG=chromium:663714
NOTRY=true
TBR=bradnelson@chromium.org,titzer@chromium.org

Review-Url: https://codereview.chromium.org/2640743004
Cr-Commit-Position: refs/heads/master@{#42467}