Disable flaky Previews tests on Linux

The tests were already disabled on Windows and Mac for being flaky (the
feature is only enabled on Android and the tests should still be running
there).

Bug: 831838
Change-Id: I14f0a97785e01033f094e75765734d33bff9a988
Reviewed-on: https://chromium-review.googlesource.com/1029179
Reviewed-by: Doug Arnett <dougarnett@chromium.org>
Commit-Queue: Tim Brown <timbrown@chromium.org>
Cr-Commit-Position: refs/heads/master@{#554209}
1 file changed