The ornamental design for a chairframe, as shown and described.
FIG. 1 is a rear elevational view of a chair frame which forms our new design, the broken lines of a chair being for illustrative purposes only and forming no part of our design;
FIG. 2 is a perspective view showing the top, left side and front thereof;
FIG. 3 is a left side elevational view thereof, this view and the opposite right side elevational view being mirror images;