title: ProgressBar inside MaterialButton
body: <p>I was looking at material design website when I got to this page about <a href="https://material.io/components/progress-indicators#circular-progress-indicators" rel="nofollow noreferrer">circular progressbar</a> and more precisely this <a href="https://kstatic.googleusercontent.com/files/0a70f74ba7b198ba734b2003bbb9af016f61c7395a78c03375a30550dc5b5d8394c5314f705e69c517c9d9b1e58ff35339cee2154197c366696d3a9a55a3c25a" rel="nofollow noreferrer">video</a></p>
  <p>I'd like to create a button like the one in the video but I don't see any documentation about this, and I don't know where to start</p>