title: How to get "?android:attr/actionBarSize" with Compatibility Library
body: <p>I'm trying to use Fragments and ActionBar in a Android 2.2 project. There is some error when using "?android:attr/actionBarSize", how to get and set that value correctly?</p>
  
  <p>Example:</p>
  
  <pre><code>&lt;LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
      android:orientation="horizontal"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:id="@+id/frags"&gt;
  
      &lt;fragment class="com.example.android.hcgallery.TitlesFragment"
              android:id="@+id/frag_title"
              android:visibility="gone"
              android:layout_marginTop="?android:attr/actionBarSize"
              android:layout_width="@dimen/titles_size"
              android:layout_height="match_parent" /&gt;
  
      &lt;fragment class="com.example.android.hcgallery.ContentFragment"
              android:id="@+id/frag_content"
              android:layout_width="match_parent"
              android:layout_height="match_parent" /&gt;
  
  &lt;/LinearLayout&gt;
  </code></pre>
  
  <p><strong>Error: No resource found that matches the given name (at 'layout_marginTop' with value '?android:attr/actionBarSize').</strong></p>