title: Get TableView Content Size Height
body: <p>i want to set height constraint to my <code>UITableView</code> so i can stretch it.
  The problem is that im not getting accurate reading with <code>tableView.contentSize.height</code>.
  My table has 10 rows when each is 40px height.
  <code>tableView.contentSize.height</code> reads as 388 while
  10 * 40 (which is the actual height is 400)</p>
  
  <p>what am i missing here?
  thanks</p>