The ornamental design for a portablegrill, as shown and described.
FIG. 1 is a perspective view showing our new design for a portable grill;
FIG. 2 is a left side view thereof;
FIG. 3 is a right side view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a front view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The broken lines depict portions of the grill that form no part of the claim. The broken lines act as boundaries of the claim where they intersect claimed surfaces.