Chair Backrest

1. Chair backrest

1 . 1 : Perspective

1 . 2 : Front

1 . 3 : Back

1 . 4 : Left

1 . 5 : Right

1 . 6 : Top

1 . 7 : Bottom

1 . 8 : Perspective

A new, original and ornamental design for a chair backrest, as shown and described; FIG. 1 . 1 is a front perspective view of a chair backrest; FIG. 1 . 2 is a front view thereof; FIG. 1 . 3 is a back view thereof; FIG. 1 . 4 is a left side view thereof; FIG. 1 . 5 is a right side view thereof; FIG. 1 . 6 is a top view thereof; FIG. 1 . 7 is a bottom view thereof; and FIG. 1 . 8 is a rear perspective view thereof. The broken lines shown in the drawings illustrate portions of the article andthat form no part of the claimed design.