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 my 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 front and left side perspective view thereof; and,
FIG. 7 is a front and right side perspective view thereof.
The rear view of the front bumper for an automobile forms no part of the claimed design. The inside surfaces of the front bumper for an automobile, shown in broken lines in FIGS. 2 and 6, form no part of the claimed design since the inside surfaces are hidden when the front bumper for an automobile is mounted to the automobile.