The ornamental design for a chairarm, as shown and described.
FIG. 1 is a left side elevational view of a chair arm which forms my new design, the broken lines in this and other figures being for illustrative purposes and forming no part of my design;
FIG. 2 is a right side elevational view thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is a rear elevational view thereof;
FIG. 5 is a front elevational view thereof; and,
FIG. 6 is a perspective view showing the left side, top and front thereof.