The ornamental design for a frontbumper for an automobile, as shown and described.
FIG. 1 is a front elevational view of a front bumper for an automobile showing our new design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a bottom plan view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a first side perspective view thereof; and,
FIG. 7 is a second side perspective view thereof.
The rear view of the front bumper forms no part of the claimed design. The inside surfaces of the front bumper, shown in broken lines in FIGS. 2, 6 and 7, form no part of the claimed design since the inside surfaces are hidden when the front bumper is mounted to the automobile.