Return a newly added `p:graphicFrame` element containing an empty
        table with *rows* rows and *cols* columns, positioned at the location
        of this placeholder and having its same width. The table's height is
        determined by the number of rows.

def _new_placeholder_table(self, rows, cols):
        """
        Return a newly added `p:graphicFrame` element containing an empty
        table with *rows* rows and *cols* columns, positioned at the location
        of this placeholder and having its same width. The table's height is
        determined by the number of rows.
        """
        shape_id, name, height = self.shape_id, self.name, Emu(rows*370840)
        return CT_GraphicalObjectFrame.new_table_graphicFrame(
            shape_id, name, rows, cols, self.left, self.top, self.width,
            height
        )