title: Error using Android Design Support Library: attr backgroundTint not found
body: <p>Trying to use the new Design Support Library in my project, AAPT throws the following error:</p>
  
  <pre><code>Description: Error: No resource found that matches the given name: attr 'backgroundTint'.
  Resource:    /design/res/values/styles.xml
  Location:    line 21 
  </code></pre>
  
  <p>This is the affected entry in <code>styles.xml</code>:</p>
  
  <pre><code>&lt;style name="Widget.Design.FloatingActionButton" parent="android:Widget"&gt;
      &lt;item name="android:background"&gt;@drawable/fab_background&lt;/item&gt;
      &lt;item name="backgroundTint"&gt;?attr/colorAccent&lt;/item&gt;
      &lt;item name="fabSize"&gt;normal&lt;/item&gt;
      &lt;item name="elevation"&gt;@dimen/fab_elevation&lt;/item&gt;
      &lt;item name="pressedTranslationZ"&gt;@dimen/fab_translation_z_pressed&lt;/item&gt;
      &lt;item name="rippleColor"&gt;?attr/colorControlHighlight&lt;/item&gt;
      &lt;item name="borderWidth"&gt;@dimen/fab_border_width&lt;/item&gt;
  &lt;/style&gt;
  </code></pre>
  
  <p>I'm targeting my project to use SDK 21, with min SDK set to 17.</p>
  
  <p><strong>Edit:</strong> I have all SDK tools up to date.</p>