identifier that determines which messages will cause a push notification to
          be sent to this client. The channel name must start with a letter and contain only
          letters, numbers, dashes, and underscores.<DD><CODE>cls</CODE> - This should be a subclass of Activity. An instance of this Activity is started when
          the user responds to this push notification. If you are not sure what to use here,
          just use your application's main Activity subclass.
<DT><B>Throws:</B>
<DD><CODE>