We claim the ornamental design for a glider rocker, as shown and described.
FIG. 1 is a perspective view of the design of the present invention for a glider rocker;
FIG. 2 is a right side view thereof; a left side view being a mirror image thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a back view thereof; and,
FIG. 5 is a top view thereof.
FIGS. 1, 2, 3, 4 and 5 illustrate with phantom lines, cushions which are shown for purposes of environment only and form no part of the claimed design.