The ornamental design for a chair, as shown and described.
FIG. 1 is a perspective view from the front side of a chair.
FIG. 2 is a perspective view from the rear side thereof.
FIG. 3 is a front elevation view thereof.
FIG. 4 is a rear elevation view thereof.
FIG. 5 is a right side elevation view thereof. A left side elevation view is omitted because it is a mirror image to the right side elevation view.
FIG. 6 is a top plan view thereof.
FIG. 7 is a bottom plan view thereof.
FIG. 8 is a perspective view from the front side thereof when it is sat on; and,
FIG. 9 is a perspective view from the rear side thereof when it is sat on.
The portions of the chair shown in broken lines is for the purpose of showing environmental structure only and form no part of the claimed design. The backrest sheet has a mesh pattern and this backrest sheet forms no part of the claimed design.