The ornamental design for a frame for an infantsupport structure, as shown and described.
FIG. 1 is a front perspective view of a frame for an infant support structure according to the present invention;
FIG. 2 is a front view of the frame for an infant support structure of FIG. 1;
FIG. 3 is a rear view of the frame for an infant support structure of FIG. 1;
FIG. 4 is a top view of the frame for an infant support structure of FIG. 1;
FIG. 5 is a bottom view of the frame for an infant support structure of FIG. 1;
FIG. 6 is a left side view of the frame for an infant support structure of FIG. 1; and,
FIG. 7 is a right side view of the frame for an infant support structure of FIG. 1.
The broken lines shown in the figures are included for the purpose of illustrating the unclaimed portions of the article and form no part of the claimed design.