The ornamental design for a chairbase, as shown and described.
FIG. 1 is a perspective view of a chair base incorporating the design of
the present invention.
FIG. 2 is a top view of the chair base.
FIG. 3 is a side view of the chair base positioned such that one of the
legs of the base is in the center of the view.
FIG. 4 is a side view of the chair base, slightly rotated from the position
shown in FIG. 3 positioned such that the center of the view is between two
legs of the base; and,