ComputeDelta takes two protos and outputs a third one that contains the difference between the two.

ComputeDeltaFromSameDevice takes two Batterystats protos taken from the same device and outputs a third one that contains the difference between the two, including fields that can only be subtracted in special cases (same device and same start clock time).

NormalizeStats takes in a proto and normalizes it by converting any absolute value to value/TotalTime.