The ornamental design for a chair, as shown and described.
FIG. 1 is a perspective view from the rear side of a chair.
FIG. 2 is a perspective view from the front side thereof.
FIG. 3 is a front elevation view thereof.
FIG. 4 is a right side elevation view thereof.
FIG. 5 is a left side elevation view thereof.
FIG. 6 is a top plan view thereof.
FIG. 7 is a rear elevation view thereof; and,
FIG. 8 is a bottom plan view thereof.
The portions of the chair shown in broken lines are for the purpose of showing environmental structure only and form no part of the claimed design. The backrest sheet is shown in front of the lumbar support in FIGS. 2, 3 and 6, and has a mesh pattern and this backrest sheet forms no part of the claimed design.