Add some more logging to settings battery stuff

This CL adds logging to areas which are possible suspects for
the slowdown some people have been reporting in the
PowerUsageAdvanced screen. It times the time it takes for various
battery stats methods as well as the time it takes to draw things.

Test: still build (only adds logging)
Bug: 62959645
Bug: 63442960
Change-Id: I7e6c5e83e33a931057c9fdef14d3bef84f514940