title: Why does visibilitychange event not fire for Android webview?
body: <p>My app has multiple android web views, in site-wide JS, I have:</p>
  
  <pre><code>window.addEventListener('beforeunload', function() {console.log("beforeunload");});
  
  // subscribe to visibility change events
  document.addEventListener('visibilitychange', function() {
      console.log('visibility changed!!!');
  }
  </code></pre>
  
  <p>Neither <code>beforeunload</code> nor <code>visibilitychange</code> fires when I (1) hit the "home" button to go to home screen or (2) invoke the task switcher to move on to different app. </p>
  
  <p>To clarify, visibilitychange gets fired in Android Chrome correctly. What's different about webviews?</p>