public static <M> Trigger<M> count(long count) {
    return new CountTrigger<M>(count);
  }
Creates a {@link Trigger} that fires when the number of messages in the pane
reaches the specified count.

@param count the number of messages to fire the trigger after
@param <M> the type of input message in the window
@return the created trigger
samza-api/src/main/java/org/apache/samza/operators/triggers/Triggers.java