title: serviceworkers focus tab: clients is empty on notificationclick
body: <p>I have a common serviceworker escenario, where I want catch a notification click and focus the tab where the notification has come from. However, clients variable is always empty, its lenght is 0</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>console.log("sw startup");
  self.addEventListener('install', function (event) {
      console.log("SW installed");
  });
  
  self.addEventListener('activate', function (event) {
      console.log("SW activated");
  });
  self.addEventListener("notificationclick", function (e) {
      // Android doesn't automatically close notifications on click 
      console.log(e);
      e.notification.close();
    
      // Focus tab if open
      e.waitUntil(clients.matchAll({
          type: 'window'
      }).then(function (clientList) {
          console.log("clients:" + clientList.length);
          for (var i = 0; i &lt; clientList.length; ++i) {
              var client = clientList[i];
              if (client.url === '/' &amp;&amp; 'focus' in client) {
                  return client.focus();
              }
          }
  
          if (clients.openWindow) {
              return clients.openWindow('/');
          }
      }));
      
  });</code></pre>
  </div>
  </div>
  </p>
  
  <p>And the registration is this one:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code> this.doNotify = function (notification) {      
          if ('serviceWorker' in navigator) {
              navigator.serviceWorker.register('sw.js').then(function (reg) {
                 
                  requestCreateNotification(notification, reg);
              }, function (err) {
                  console.log('sw reg error:' + err);
              });
          }
     ...
     }</code></pre>
  </div>
  </div>
  </p>
  
  <p>chrome://serviceworker-internals/ output shows that registration and installation are fine. However, when a notification is pushed,  clientList is empty. I have tried removing the filter type:'window' but the result is still the same. As clients are empty, a new window is always opened. What am I doing wrong?</p>