We claim the ornamental design for a window frame, as shown and described.
FIG. 1 is a left side and front perspective view of a window frame of the claimed design;
FIG. 2 is a cross-sectional view taken along line 2—2 in FIG. 1;
FIG. 3 is a front view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The ornamental design which is claimed is shown in solid lines in the drawings. The broken lines in the drawings are for illustrative purposes only and form no part of the claimed design.