title: Get ProgressBar to fill StatusBarItem
body: <p>I have a <code>StatusBar</code> that I'd like to house a <code>TextBlock</code> docked to the left and a <code>ProgressBar</code> filling the remaining width. In all my other experiences with the WPF <code>ProgressBar</code>, it will fill its given container, however in this situation it doesn't auto-size at all, it just appears as a tiny circle. Setting its height and width manually work fine, but I'd like it to scale to the remaining width of the <code>StatusBar</code>.</p>
  
  <p>Here's my XAML for the <code>StatusBar</code>:</p>
  
  <pre><code>&lt;StatusBar DockPanel.Dock="Bottom" Height="25"&gt;
      &lt;StatusBarItem DockPanel.Dock="Left"&gt;
          &lt;TextBlock x:Name="lblStatus"  Margin="5,0,0,0"/&gt;
      &lt;/StatusBarItem&gt;
      &lt;StatusBarItem&gt;
          &lt;ProgressBar x:Name="pgbStatus" /&gt;
      &lt;/StatusBarItem&gt;
  &lt;/StatusBar&gt;
  </code></pre>