'Given the list of ticks, return two lists of bboxes. One for
tick lable1\'s and another for tick label2\'s.'

def _get_tick_bboxes(self, ticks, renderer):

    ticklabelBoxes = []
    ticklabelBoxes2 = []
    for tick in ticks:
        if (tick.label1On and tick.label1.get_visible()):
            extent = tick.label1.get_window_extent(renderer)
            ticklabelBoxes.append(extent)
        if (tick.label2On and tick.label2.get_visible()):
            extent = tick.label2.get_window_extent(renderer)
            ticklabelBoxes2.append(extent)
    return (ticklabelBoxes, ticklabelBoxes2)
