[Night Light] CL2: Ash and system tray work
Add ash and system tray initial plumbing. Support only toggling
NightLight on / off and setting the temperature to a fixed 0.5f
value when it's turned on for now.
Follow-up CLs will add system settings support.
Demo: https://bugs.chromium.org/p/chromium/issues/detail?id=705816#c4
BUG=705816
TEST=System tray has a toggle button. NightLight turns on / off with
a 2-second animation. When on, a tray icon shows next to the
clock and battery.
Review-Url: https://codereview.chromium.org/2857103007
Cr-Commit-Position: refs/heads/master@{#470392}
27 files changed
