[LUCI] increase linux_chromium_headless_rel percentage to 100%

TBR=jbudorick@chromium.org

Bug: 731559
Change-Id: I6ce427c4dfe389a7859a3d21afe2130da09abca4
Reviewed-on: https://chromium-review.googlesource.com/1076969
Reviewed-by: Shenghua Zhang <shenghuazhang@chromium.org>
Commit-Queue: Shenghua Zhang <shenghuazhang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#562515}
1 file changed