'Update the scroll-regions for each canvas.  This ensures that
everything is within a scroll-region, so the user can use the
scrollbars to view the entire display.  This does *not*
resize the window.'

def _resize(self):

    c = self._chart_canvas
    width = ((self._chart.num_leaves() * self._unitsize) + (ChartView._MARGIN * 2))
    levels = len(self._edgelevels)
    self._chart_height = ((levels + 2) * self._chart_level_size)
    c['scrollregion'] = (0, 0, width, self._chart_height)
    if self._tree_canvas:
        self._tree_canvas['scrollregion'] = (0, 0, width, self._tree_height)
