title: Shrink container to smaller child rather than expanding to fill parent
body: <p>I'm creating a custom widget for a segment control.</p>
  
  <pre><code>return Padding(
    padding: const EdgeInsets.symmetric(vertical: 20.0),
    child: Container(
      decoration: BoxDecoration(border: Border.all(color: Colors.blue)),
      child: Row(
        mainAxisSize: MainAxisSize.min,
        children: buttons,
      ),
    ),
  );
  </code></pre>
  
  <p>I want the container to shrink to the minimum size to contain its children.  However when I include the widget in a parent, it expands to fill the parent.  This is visible because the border from the decoration is larger than the buttons.</p>
  
  <p>How do I force the container to shrink?</p>