The ornamental design for an officechairmechanism, as shown and described.
FIG. 1 is a front elevation view of the office chair mechanism showing my new design;
FIG. 2 is a left side elevation view thereof;
FIG. 3 is a top plan view thereof; and,
FIG. 4 is a perspective view thereof.
The broken lines shown in the drawing represent portions of the office chair armrest that form no part of the claimed design; further, the broken lines illustrate the claim in use and form no part of the claimed design.