title: Android: Images of GroupIndicator in ExpandableListview not show fine
body: <p>I have created an app with a custom <code>ExpandableListView</code>. I have wanted to put an images in groupIndicator to left. But I get that the images show elongated to right. The size of the images is 100x100 px. How I can adjust the width of the images to the size of the expandable row?</p>
  
  <p><strong>main.xml</strong></p>
  
  <pre><code>&lt;ExpandableListView
                      android:id="@+id/expandable"
                      style="@style/scrollbar"
                      android:layout_width="match_parent"
                      android:layout_height="match_parent"
                      android:groupIndicator="@drawable/expandable"
                      android:listSelector="@color/negro"
                      android:adjustViewBounds="true"
                      android:padding="0dp"
                      android:scrollingCache="false" /&gt;
  </code></pre>
  
  <p><strong>expandable.xml</strong></p>
  
  <pre><code>&lt;selector xmlns:android="http://schemas.android.com/apk/res/android"&gt;
    &lt;item android:drawable="@drawable/expandable_icono_abajo" android:state_empty="true"/&gt;
    &lt;item android:drawable="@drawable/expandable_icono_arriba" android:state_expanded="true"/&gt;
    &lt;item android:drawable="@drawable/expandable_icono_abajo" /&gt;
  &lt;/selector&gt;
  </code></pre>