Observable: Clean up and generify observable.

- Use ArrayList<Observer> instead of Vector

- Clearer variable names. (|observers| instead of |obs|). This also
  fixes issues with apps that were dependant on the name of this
  variable. I emphasize here that this change is only being made because
  the new variable name is cleaner. Apps must NOT depend on private
  implementation details.

bug: 26937230
Change-Id: I0757157ccb158e400a9513a1464b19298b465233
1 file changed