Introduce --force-devtools-available for Chrome OS

The --force-devtools-available flag can be used for autotest on Chrome OS
devices, because autotest tends to rely on devtools remote inspection,
so disabled devtools can break autotest.
It is only possible to change command-line flags in developer mode on
Chrome OS devices.

Bug: 838146
Test: browser_tests --gtest_filter=DevToolsAllowedByCommandLineSwitch*
Change-Id: Ic45aaa618dae522adcce41a3e8d20c4c68b54dc7
Reviewed-on: https://chromium-review.googlesource.com/1141742
Commit-Queue: Pavol Marko <pmarko@chromium.org>
Reviewed-by: Maksim Ivanov <emaxx@chromium.org>
Reviewed-by: Pavel Feldman <pfeldman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576217}
4 files changed