DebugNotificationListener.start(DebugNotification) this is
invokedObservable chain to emit a detailed account of all the events
that happened.RxJavaPlugins registerObservableExecutionHook(hook) method.DebugHook to receive notification
about all activity in Rx.DebugNotificationListener.start(DebugNotification)
this is invokedDebugNotification.Kind start is invoked before the actual method is invoked.