Merge "Improve threading docs for TimeZoneProviderService"

 *

 * <p>Threading:

 *

 * <p>Calls to {@code report} methods can be made on on any thread and will be passed asynchronously

 * to the system server. Calls to {@link #onStartUpdates(long)} and {@link #onStopUpdates()} will

 * occur on a single thread.

 * <p>Outgoing calls to {@code report} methods can be made on any thread and will be delivered

 * asynchronously to the system server. Incoming calls to {@link TimeZoneProviderService}-defined

 * service methods like {@link #onStartUpdates(long)} and {@link #onStopUpdates()} are also

 * asynchronous with respect to the system server caller and will be delivered to this service using

 * a single thread. {@link Service} lifecycle method calls like {@link #onCreate()} and {@link

 * #onDestroy()} can occur on a different thread from those made to {@link

 * TimeZoneProviderService}-defined service methods, so implementations must be defensive and not

 * assume an ordering between them, e.g. a call to {@link #onStopUpdates()} can occur after {@link

 * #onDestroy()} and should be handled safely.

 *

 * @hide

 */