Unified: Hide inactive top buttons instead of dim.

On the login screen, we made the settings button and the lock button
look dim.

According to UX, we should just make them invisible.

TEST=manual
BUG=864233

Change-Id: I90fc6853b2735a73d426dbb05b2f693be7ff2ce6
Reviewed-on: https://chromium-review.googlesource.com/1139847
Reviewed-by: Yoshiki Iguchi <yoshiki@chromium.org>
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575970}
2 files changed