title: UITableViewCell's contentView's width with a given accessory type
body: <p>On an iPhone, how do you figure out the width of a table view cell's content view when it is showing a certain accessory view (disclosure indicator, etc)?</p>
  
  <p>I need this in order to calculate the correct cell height for cells that contain wrapping, variable-length text.  But when the table view delegate is asked for a cell height, it doesn't actually have the actual cell instance, so it can't just query the content view bounds directly.</p>
  
  <p>I can easily hard-code a 20-pixel margin on the right which appears to be accurate for a plain style table view in portrait orientation with a disclosure indicator, but would prefer to do it the Right Way so that it keeps working if Apple decides to tweak the margin.</p>
  
  <p>(This is related to <a href="https://stackoverflow.com/questions/494562/setting-custom-uitableviewcells-height">this question</a>.)</p>