chromeos: make ozone the default

X11 is no longer used on any machines and X11 for chromeos will soon be removed entirely. So, switch the default for chromeos to use_ozone. All the builders explicitly specify what config they want, so there shouldn't be any changes needed there.

BUG=722539
TEST=none
R=brettw@chromium.org

Review-Url: https://codereview.chromium.org/2895523002
Cr-Commit-Position: refs/heads/master@{#473237}
1 file changed