The ornamental design for a flask for cosmetic, as shown and described.
FIG. 1 is a front view of a flask for cosmetic showing the new design, the rear view being a mirror image thereof.
FIG. 2 is a top view thereof.
FIG. 3 is a bottom view thereof.
FIG. 4 is an enlarged right side view thereof.
FIG. 5 is an enlarged left side view thereof.
FIG. 6 is a front, bottom and left side perspective view thereof.
FIG. 7 is a front, top and left side perspective view thereof; and,
FIG. 8 is a front view thereof with left and right central end members extended from a remainder of the associated end as occurs after a rotation of one end relative to the other end about a longitudinal axis of the flask.