title: Gravity of BitmapDrawable doesn't work
body: <p>I have a <code>BitmapDrawable</code> in xml:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;bitmap xmlns:android="http://schemas.android.com/apk/res/android"
          android:antialias="true"
          android:autoMirrored="true"
          android:dither="true"
          android:gravity="bottom"
          android:filter="true"
          android:src="@drawable/test"
  /&gt;
  </code></pre>
  
  <p>I used this bitmap for a Imageview like below:</p>
  
  <pre><code>&lt;ImageView android:id="@+id/detail_img"
             android:layout_width="match_parent"
             android:layout_height="match_parent"
             android:background="@color/colorAccent"
             android:src="@drawable/bitmap_drawable"/&gt;
  </code></pre>
  
  <p>The result:<br>
  <a href="https://i.stack.imgur.com/cbCUh.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/cbCUh.png" alt="enter image description here"></a><br>
  You can see there is some padding in top and bottom. And the bitmap didn't aligned to bottom of the imageview, but I set <code>android:gravity="bottom"</code> in the bitmap xml.
  I also tried <code>android:gravity="top"</code>, It also didn't work. 
  What's wrong with my code. I googled, but didn't find anything about it.</p>
  
  <p>I just want to know why the <code>gravity</code> property in bitmap xml didn't work.</p>
  
  <p>Thanks in advance.</p>
  
  <hr>
  
  <p>I know I can set <code>android:scaleType="fitEnd"</code> to the imageview which can let the imageview alignd to bottom.</p>