Inspector may change protocol and it can end up with broken headless
bot.

R=dgozman@chromium.org

Bug: none
Cq-Include-Trybots: luci.chromium.try:linux_chromium_headless_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Ia813ecebcd509d66ac2291d2836f556e8fb3a096
Reviewed-on: https://chromium-review.googlesource.com/1081338Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53463}