function getLinesFromRects(el, lineHeight) {
    var rects = el.getClientRects();
    var lines = 0;

    each(rects, function(rect) {
      lines += lineCount(rect.height, lineHeight);
    });

    return lines;
  }
Returns total line
count from a rect list.

@param  {Element} el
@param  {Number} lineHeight
@return {Number}
@api private