Called by the framework when a checklist box with a nondefault style is created.
A long pointer to a MEASUREITEMSTRUCT structure.
By default, this member function does nothing. Override this member function and fill in the MEASUREITEMSTRUCT structure to inform Windows of the dimensions of checklist-box items. If the checklist box is created with the LBS_OWNERDRAWVARIABLE style, the framework calls this member function for each item in the list box. Otherwise, this member is called only once.