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 in accordance with my new design;
FIG. 2 is a rear elevational view of the front bumper for an automobile in accordance with my new design;
FIG. 3 is a top plan view of the front bumper for an automobile in accordance with my new design;
FIG. 4 is a bottom plan view of the front bumper for an automobile in accordance with my new design;
FIG. 5 is a left side elevational view of the front bumper for an automobile in accordance with my new design;
FIG. 6 is a right side elevational view of the front bumper for an automobile in accordance with my new design; and,
FIG. 7 is a perspective view of the front bumper for an automobile in accordance with my new design.
The broken line showing of the front bumper for an automobile is for purpose of illustrating environmental structure and forms no part of the claimed design.