title: android:layout_height="?attr/actionBarSize" is not working with support:design:23.0.0' library
body: <p>If I set <code>android:layout_height="56dp"</code>, I can see the toolbar in graphical layout. But when I set like the below,</p>
  
  <pre><code>       &lt;android.support.v7.widget.Toolbar
              android:id="@+id/toolbar"
              android:layout_width="match_parent"
              android:layout_height="?attr/actionBarSize"
              android:background="@color/purple"
              android:gravity="center_vertical"
              android:minHeight="?attr/actionBarSize"
              app:layout_scrollFlags="scroll|enterAlways"
              app:popupTheme="@style/ThemeOverlay.AppCompat.Light"&gt;  &lt;/android.support.v7.widget.Toolbar&gt;
  </code></pre>
  
  <p>toolbar is not showing in graphical layout. </p>
  
  <p>Studio says that <code>attr/actionBarSize</code> is marked as private. </p>
  
  <p>I am using </p>
  
  <pre><code> compile 'com.android.support:appcompat-v7:23.0.0'
   compile 'com.android.support:design:23.0.0'
  </code></pre>
  
  <p>What could be the issue? How can i fix it! Yes, Studio is updated.</p>