Mark the x64 official tests executable as optional in files.cfg.
Mark the x64 official tests executable as optional in files.cfg.

We don't build these tests anymore on this builder.

R=govind@chromium.org,sebmarchand@chromium.org

Review-Url: https://codereview.chromium.org/2021953003
Cr-Commit-Position: refs/heads/master@{#396871}
(cherry picked from commit 966c665e43df27a614646f30cf24c262365eced6)

Review URL: https://codereview.chromium.org/2034253002 .

Cr-Commit-Position: 03d981dee550804c6934fd1a1d9cfa3c172affd3@{#210}
Cr-Branched-From: e9621a186760eb36d74098d9e33e4dd91c427b34@{#394939}

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk