This change simplifies the process of initializing a SystemService
by folding the onCreate() step back into the constructor. It removes
some ambuiguity about what work should happen in the constructor and
should make it possible for services to retain most of their final
fields after refactoring into the new pattern.
Change-Id: I25f41af0321bc01898658ab44b369f9c5d16800b
b880d880c6