The ornamental design for a chairarmrest, as shown and described.
FIG. 1 is a perspective view of the chair armrest showing my new design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a left side elevation view thereof;
FIG. 5 is a right side elevation view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof;
FIG. 8 is another perspective view showing the chair armrest on a backrest unit. The chair backrest is shown in broken lines for illustrative purposes only and forms no parts of the claimed design; and,
FIG. 9 is another perspective view of the armrest shown in use with chair backrest which is shown in broken lines. The broken lines are for illustrative purposes only and form no part of the claimed design.