GitLab

If a display power change request arrives before the previous one
finishes or if a previous power change request failed the state becomes
inconsistent and future requests are optimized out.

BUG=627795
TEST=New unittest in display_unittests and manually checked on Samus

Review-Url: https://codereview.chromium.org/2154743003
Cr-Commit-Position: refs/heads/master@{#405990}