The ornamental design for a cosmeticbrush, as shown and described.
FIG. 1 is a perspective view of a cosmetic brush showing my new design;
FIG. 2 is a front elevatlonal view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken line showing a brush head and a ferrule is included for the purpose of illustrating use and environment and forms no part of the claimed design.