title: What is the default interpolator if android:interpolator is unspecified
body: <p>In Android, I know we can define animations via XML.</p>
  
  <p>For example, <code>scale_button_up.xml</code> might look something like</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;set xmlns:android="http://schemas.android.com/apk/res/android"
       android:interpolator="@android:anim/linear_interpolator"
       android:fillBefore="true"
       android:fillAfter="true"
       android:fillEnabled="true"&gt;
      &lt;scale
          android:duration="5000"
          android:fromXScale="0.25"
          android:fromYScale="0.25"
          android:pivotX="50%"
          android:pivotY="50%"
          android:toXScale="0.75"
          android:toYScale="0.75"/&gt;
  &lt;/set&gt;
  </code></pre>
  
  <p>I was wondering what the default behaviour is for Android V21+, if <code>android:interpolator="@android:anim/linear_interpolator"</code> were not specified.</p>