title: owner._debugCurrentBuildTarget == this , is not true
body: <p>[on web] tried to fit some widgets inside a <code>FittedBox</code> like this :</p>
  
  <pre><code> FittedBox(
     fit: BoxFit.scaleDown,
     child: AnimatedContainer(...)
   )
  </code></pre>
  
  <p>but screen and console show only this message :</p>
  
  <p><a href="https://i.stack.imgur.com/iHn5T.png" rel="noreferrer"><img src="https://i.stack.imgur.com/iHn5T.png" alt="error"></a></p>
  
  <p>there's nothing else in the console</p>
  
  <p>what's the next step here ? :D</p>