The ornamental design for a mirror, as shown and described.
FIG. 1 is a front elevational view of a mirror showing my new design;
FIG. 2 is a right side elevational view thereof; and
FIG. 3 is a top plan view thereof.
The unshown rear of the design is substantially the same as what is shown
in FIG. 1 except that the rectangular area comprising the mirror and the
rectangular area above the mirror are flat plain and unornamented.