title: Hardcoded manifest start url still not found?
body: <p>I am attempting to setup a WordPress Theme as a Progressive Web App. When I run Chromes Audit tool (lighthouse?) I get an uninformative error that I don't know what exactly the problem is. The error is:</p>
  
  <blockquote>
    <p>Failures: Service worker does not successfully serve the manifest start_url. Unable to fetch start url via service worker</p>
  </blockquote>
  
  <p>I have hardcoded my start url which is a valid url. Any suggestions on what the issue could be?</p>
  
  <p><code>https://mywebsite.com/wp-content/themes/mytheme/web.manifest</code>:</p>
  
  <pre><code>  ...
    "scope": "/",
    "start_url": "https://mywebsite.com",
    "serviceworker": {
      "src": "dist/assets/sw/service-worker.js",
      "scope": "/aw/",
      "update_via_cache": "none"
    },
    ...
  }
  </code></pre>
  
  <p><code>https://mywebsite.com/wp-content/themes/mytheme/dist/assets/sw/service-worker.js</code>:</p>
  
  <pre><code>...
  // The fetch handler serves responses for same-origin resources from a cache.
  // If no response is found, it populates the runtime cache with the response
  // from the network before returning it to the page.
  self.addEventListener('fetch', event =&gt; {
    // Skip cross-origin requests, like those for Google Analytics.
    if (event.request.url.startsWith(self.location.origin)) {
      event.respondWith(
        caches.match(event.request).then(cachedResponse =&gt; {
          if (cachedResponse) {
            return cachedResponse;
          }
  
          return caches.open(RUNTIME).then(cache =&gt; {
            return fetch(event.request).then(response =&gt; {
              // Put a copy of the response in the runtime cache.
              return cache.put(event.request, response.clone()).then(() =&gt; {
                return response;
              });
            });
          });
        })
      );
    }
  });
  </code></pre>
  
  <p>I register my SW with the following code and it outputs that it has successfully registered the SW:</p>
  
  <pre><code>if ('serviceWorker' in navigator) {
    navigator.serviceWorker.register(Vue.prototype.$ASSETS_PATH + 'sw/service-worker.js')
    .then(function(registration) {
      console.log('Registration successful, scope is:', registration.scope);
    })
    .catch(function(error) {
      console.log('Service worker registration failed, error:', error);
    });
  }
  </code></pre>