The ornamental design for a frontgrill for an automobile, as shown and described.
FIG. 1 is a front perspective view of a front grill for an automobile of my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a top plan view thereof;
FIG. 5 is a bottom plan view thereof;
FIG. 6 is a left-side view thereof; and,
FIG. 7 is a right-side view thereof.
A second embodiment of the design is the design of FIGS. 1-7, without the rear view of FIG. 3. Thus, the second embodiment of the design is depicted in FIGS. 1, 2, and 4-7.