'Create and return a new GridlineCollection instance.
*which* : "major" or "minor"
*axis* : "both", "x" or "y"'

def new_gridlines(self, grid_helper=None):

    if (grid_helper is None):
        grid_helper = self.get_grid_helper()
    gridlines = grid_helper.new_gridlines(self)
    return gridlines
