display: Validate content protection requests

DisplayConfigurator clients are responsible for renewing their content
protection requests when the display configuration changes, as pending
tasks will be killed on reconfiguration in a future CL.

This CL invokes the failure callback for requests whose display is
invalid.

Bug: 929449
Test: display_unittests
Change-Id: I74d247b8532a7072d7852903d1ce4c4e5006f1c1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1554004
Commit-Queue: Dominik Laskowski <domlaskowski@chromium.org>
Reviewed-by: Daniel Nicoara <dnicoara@chromium.org>
Cr-Commit-Position: refs/heads/master@{#649276}