We claim the ornamental design for a mirror assembly, as shown and described.
FIG. 1 is a perspective view of my new design of a mirror assembly;
FIG. 2 is a front view of my design shown in FIG. 1;
FIG. 3 is a rear view of my design shown in FIG. 1;
FIG. 4 is a side view of my design shown in FIG. 1;
FIG. 5 is a top view of my design shown in FIG. 1; and,
FIG. 6 is a bottom view of my design shown in FIG. 1.
The ornamental design which is claimed is shown in solid lines in the drawings. In the drawings, the broken lines depict a vehicle and form no part of the claimed design.