The ornamental design for a chairframe, as shown and described.
FIG. 1 is a perspective view of a chair frame showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a left side elevational view thereof;
FIG. 4 is a right side elevational view thereof;
FIG. 5 is a rear elevational view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is an exploded perspective view of thereof in an environment showing other chair frames.
The broken lines showing additional chair frames in FIG. 8 represent are environmental and form no part of the claimed design. All other broken lines show portions of a chair frame that form no part of the claimed design.