The ornamental design for a chandelier arm, as shown and described.
FIG. 1 is a left side view of a chandelier arm with attached star-shaped surface ornaments and an attached light fixture element shown in phantom, the right side view being a mirror image thereof;
FIG. 2 is a side, front view of the chandelier arm shown attached to a chandelier, with all other elements of the chandelier shown in phantom; and,
FIG. 3 is a side, front view of the chandelier arm also shown attached a chandelier, with beads in a frame of the arm and all other elements of the chandelier shown in phantom.
The broken lines are shown for illustrative purposes only and form no part of the claimed design.