title: Align a group of views containing a chain in a ConstraintLayout
body: <p>I have three views in a ConstraintLayout and want to align then like this:</p>
  
  <p><a href="https://i.stack.imgur.com/3az1I.png" rel="noreferrer"><img src="https://i.stack.imgur.com/3az1I.png" alt="enter image description here"></a></p>
  
  <p>Right now views <strong>B</strong> and <strong>C</strong> form a vertical chain, and <strong>A</strong> is centered relative to the chain. But how do I align the entire group centered in the parent? Note that View <strong>C</strong> may be <code>GONE</code>.</p>