This CL introduces a set of configuration options implemented as
a struct of booleans that together comprise the set of enabled
or detected features. The configuration options replace command-line
flags that were checked deep in the implementation. As such, it is
necessary to plumb them through multiple levels of abstraction.

R=ahaas@chromium.org
CC=mstarzinger@chromium.org
BUG=chromium:868844

Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: I1b82f5826e4fd263f68e8cafcd923bac5818a637
Reviewed-on: https://chromium-review.googlesource.com/1163670Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55018}