title: Seekbar progressdrawable not work correctly below Android M
body: <p>I have a seekbar whose height is <code>16dp</code>.</p>
  
  <pre><code>minHeight="16dp"
  maxHeight="16dp"
  </code></pre>
  
  <p>Now I have to use custom progress drawable.</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;layer-list xmlns:android="http://schemas.android.com/apk/res/android"&gt;
  &lt;item android:id="@android:id/background"&gt;
      &lt;shape android:shape="rectangle"&gt;
          &lt;solid android:color="xxx"/&gt;
          &lt;corners android:radius="6dp"/&gt;
      &lt;/shape&gt;
  &lt;/item&gt;
  
  &lt;item
      android:id="@android:id/secondaryProgress"
      android:bottom="4dp"
      android:left="4dp"
      android:right="4dp"
      android:top="4dp"&gt;
      &lt;clip&gt;
          &lt;shape android:shape="rectangle"&gt;
              &lt;solid android:color="xxx"/&gt;
              &lt;corners android:radius="4dp"/&gt;
          &lt;/shape&gt;
      &lt;/clip&gt;
  &lt;/item&gt;
  
  &lt;item
      android:id="@android:id/progress"
      android:bottom="4dp"
      android:left="4dp"
      android:right="4dp"
      android:top="4dp"&gt;
      &lt;clip&gt;
          &lt;shape android:shape="rectangle"&gt;
              &lt;solid android:color="xxx"/&gt;
              &lt;corners
                  android:radius="4dp"/&gt;
          &lt;/shape&gt;
      &lt;/clip&gt;
  &lt;/item&gt;
  </code></pre>
  
  <p></p>
  
  <p>As you see, I use <code>left</code>,<code>top</code>,<code>right</code>,<code>bottom</code> to insert <code>progress</code> and <code>secondaryProgress</code>. </p>
  
  <p><strong>It works well above Android M</strong>,however below Android M,the porgress and secondaryProgress fills the <code>background</code> in other word the <code>background</code> item is covered by <code>progress</code> and <code>secondaryProgress</code>.<strong>But I want progress and secondaryProgress smaller than background item.</strong></p>