The ornamental design for chair, as shown and described.
1. Chair
Reproduction 1.1 is a front view of the chair; reproduction 1.2 is a back view of the chair; reproduction 1.3 is a top view of the chair; reproduction 1.4 is a bottom view of the chair; reproduction 1.5 is a right side elevational view of the chair; a left side elevational view is with omitted because it is a mirror image of the right side elevational view; reproduction 1.6 is a cross-sectional view vertically sectioned at center of the chair; the reproduction 1.7 is an enlarged fragmentary view of the reproduction 1.6; the reproduction 1.8 is an enlarged fragmentary end view vertically sectioned at the center of reproduction 1.5; reproduction 1.9 is a front perspective view of the chair; reproduction 1.10 is a back perspective view of the chair.