Properly synchronize interactivity state.

Volatile doesn't provide any guarantees with respect to write
visibility, so it's possible that PowerManager will tell InputManager
about a change in interactivity state, but the actual dispatching
thread will never observe it.

Also, add logging about NativeInputManager state.

Bug: 22422588
Change-Id: Ifc3add992b9009d920d80a0315ff89c9574be20d