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