display: Introduce ContentProtectionManager

This CL encapsulates content protection logic in DisplayConfigurator so
it can be extended and tested in isolation.

Bug: 929449
Test: display_unittests
Change-Id: I7511e6b67d10738ce13d2c067ee492c153078432
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1663028
Reviewed-by: Daniel Nicoara <dnicoara@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Dominik Laskowski <domlaskowski@chromium.org>
Cr-Commit-Position: refs/heads/master@{#670908}