title: add to home screen not showing up PWA
body: <p>I've created a Progressive Web App.
  It's simple, just an index.html, a folder "images" with favicon etc, a sw.js et a styles.css</p>
  
  <p>My code from manifest.json</p>
  
  <pre><code>{
  "lang" : "en",
  "name" : "Test",
  "short_name" : "Test",
  "icons" :   [
    {
    "src": "images/android-chrome-192x192.png",
    "sizes": "192x192",
    "type": "image/png"
  },
  {
    "src": "images/android-chrome-144x144.png",
    "sizes": "144x144",
    "type": "image/png"
  }
  ],
  "theme_color" : "#116b20",
  "background_color" : "#1a1a1a",
  "scope" : "1",
  "start_url" : "/test",
  "display" : "standalone",
  "orientation" : "natural"
     }
  </code></pre>
  
  <p>and  sw.js</p>
  
  <pre><code>self.addEventListener('install', function(event) {
    console.log('[Service Worker] Installing Service Worker ...', event);
  event.waitUntil(
  caches.open('static').then(function(cache) {
   cache.addAll(['/test/', '/test/index.html', '/test/manifest.json']);
    })
    );
  });
  self.addEventListener('activate', function(event) {
   console.log('[Service Worker] Activating Service Worker ....', event);
  });
  self.addEventListener('fetch', function(event) {
    event.respondWith(
  caches.match(event.request).then(function(response) {
    if (response) {
      return response;
    } else {
      return fetch(event.request).then(function(res) {
        return caches.open('dynamic').then(function(cache) {
          cache.put(event.request.url, res.clone());
          return res;
        });
      });
    }
  })
    );
  });
  </code></pre>
  
  <p>So... for now, when I go to the site from my smartphone with chrome, everything is displayed correctly, the tab color is good, everythings looks good etc. But I do not have the banner "add to the home screen".
  By cons when I go in the settings of chrome, and I click on "Add to the home screen" and I validate and then I go to the added shortcut, the site is launched as an app, with the "splash screen" etc.</p>
  
  <p>And when I go on the site from my computer and I watch the debugger in "Application" and manifest, I have the little link "Add to the home screen"
  Do you know where this may come from ?</p>
  
  <p>Thanks for help !</p>
  
  <p>Edit :</p>
  
  <p>I have advanced a little
  I modified a little my organization, I created a subdomain, I now have a URL like this: <a href="https://subdomain.example.com" rel="noreferrer">https://subdomain.example.com</a>. Everything is at the root of the subdomain, in the code, the links are in relative (e.g.: "img / name.png").
  I do not have any errors in the service worker, when I go on Chrome from my pc, I go to dev tools -> Application -> Manifest tab, and I click on "Add to home screen", the banner to add the site to applications appears well
  and when I validate, it works well.
  That's what I have when I go on Chrome dev tools -> Application -> Service worker tab </p>
  
  <p><a href="https://i.stack.imgur.com/Zz6p5.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/Zz6p5.jpg" alt="sw.js"></a></p>
  
  <p>But on my smartphone, I still don't have the banner offering add to home screen, if someone has an idea...</p>