scroll-with-bottom-base

If bottom-base scrolling is on, then scroll positions are determined by line boundaries aligned with the bottom of the viewable area (rather than with the top of the viewable area). If last-line scrolling is also enabled (see allow-scroll-to-last), then the buffer is bottom-aligned in the viewing area even when the buffer does not fill the viewable area.

• (send a-wx:media-canvas scroll-with-bottom-base on?) -> void
      on? : boolean

  If on? is #f, bottom-based scrolling is disabled, otherwise it is enabled.