In a food processor, pulse the chicken until finely chopped. Add the egg white and pulse until blended. With the machine on, add the cream in a steady stream and puree until smooth. Scrape the mousse into a bowl and stir in the parsley, chives, tarragon and white pep-per. Transfer the mousse to a resealable plastic bag and refrigerate until chilled, about 1 hour. To use, snip off a corner of the bag.