Make Power Control widget a bit more responsive.

Based on a lot of timings on Sapphire.

Also, initially this CL improved the speed of Toasts, but now it just
removes the use of Toasts in the widget after eng/UX discussions with
various people.

BUG=2535155

Change-Id: I134a730f17ebee8a119b7796984f00b22e0d6120