title: Android Studio 2.2 Constraint Layout Buttons not visible
body: <p>Recently I was going through the tutorials of constraint layout (new in Android Studio 2.2). In the tutorials they had buttons used for constraints layout on the bar but there are no buttons in my Android Studio. See image below:   </p>
  
  <p><a href="https://i.stack.imgur.com/EVM6U.png" rel="noreferrer"><img src="https://i.stack.imgur.com/EVM6U.png" alt="enter image description here"></a></p>