More CPU speed stepping happening with newer devices, so we need
to qualify CPU time with the CPU speed, since power consumption
varies greatly by speed. Apps that peg the CPU should get a higher
penaltly.
Also, fix for 2062930: NPE at VolumePreference.onKey()
Track the foreground CPU time of an activity so that we can tell if apps are
spending more time in the background compared to foreground.
Update power profile values for screen backlight and GPS.
Fix some javadoc bugs (milliseconds vs. microseconds).
