Update demo project

@@ -254,10 +254,9 @@ gh-social: all
 	cd test; $(DART_BIN) --enable-asserts github_social_preview.dart
 
 gh-pages: all
-	cd demo; $(FLUTTER_BIN) build web
+	cd demo; $(FLUTTER_BIN) build web --base-href "/dart_pdf/"
 	git checkout gh-pages
 	rm -rf assets icons
 	mv -fv demo/build/web/* .
-	sed -e 's|<base href="/">|<base href="/dart_pdf/">|' -i index.html
 
 .PHONY: test format format-dart format-clang clean publish-pdf publish-printing analyze ref

@@ -8,10 +8,13 @@
     The path provided below has to start and end with a slash "/" in order for
     it to work correctly.
 
-    Fore more details:
+    For more details:
     * https://developer.mozilla.org/en-US/docs/Web/HTML/Element/base
+
+    This is a placeholder for base href that will be replaced by the value of
+    the `--base-href` argument provided to `flutter build`.
   -->
-  <base href="/">
+  <base href="$FLUTTER_BASE_HREF">
 
   <meta charset="UTF-8">
   <meta content="IE=Edge" http-equiv="X-UA-Compatible">
@@ -20,7 +23,7 @@
   <!-- iOS meta tags & icons -->
   <meta name="apple-mobile-web-app-capable" content="yes">
   <meta name="apple-mobile-web-app-status-bar-style" content="black">
-  <meta name="apple-mobile-web-app-title" content="printing_demo">
+  <meta name="apple-mobile-web-app-title" content="Flutter PDF Demo">
   <link rel="apple-touch-icon" href="icon-192.png">
 
   <!-- Favicon -->
@@ -34,16 +37,68 @@
        application. For more information, see:
        https://developers.google.com/web/fundamentals/primers/service-workers -->
   <script>
+    var serviceWorkerVersion = null;
+    var scriptLoaded = false;
+    function loadMainDartJs() {
+      if (scriptLoaded) {
+        return;
+      }
+      scriptLoaded = true;
+      var scriptTag = document.createElement('script');
+      scriptTag.src = 'main.dart.js';
+      scriptTag.type = 'application/javascript';
+      document.body.append(scriptTag);
+    }
+
     if ('serviceWorker' in navigator) {
-      window.addEventListener('flutter-first-frame', function () {
-        navigator.serviceWorker.register('flutter_service_worker.js');
+      // Service workers are supported. Use them.
+      window.addEventListener('load', function () {
+        // Wait for registration to finish before dropping the <script> tag.
+        // Otherwise, the browser will load the script multiple times,
+        // potentially different versions.
+        var serviceWorkerUrl = 'flutter_service_worker.js?v=' + serviceWorkerVersion;
+        navigator.serviceWorker.register(serviceWorkerUrl)
+          .then((reg) => {
+            function waitForActivation(serviceWorker) {
+              serviceWorker.addEventListener('statechange', () => {
+                if (serviceWorker.state == 'activated') {
+                  console.log('Installed new service worker.');
+                  loadMainDartJs();
+                }
+              });
+            }
+            if (!reg.active && (reg.installing || reg.waiting)) {
+              // No active web worker and we have installed or are installing
+              // one for the first time. Simply wait for it to activate.
+              waitForActivation(reg.installing || reg.waiting);
+            } else if (!reg.active.scriptURL.endsWith(serviceWorkerVersion)) {
+              // When the app updates the serviceWorkerVersion changes, so we
+              // need to ask the service worker to update.
+              console.log('New service worker available.');
+              reg.update();
+              waitForActivation(reg.installing);
+            } else {
+              // Existing service worker is still good.
+              console.log('Loading app from service worker.');
+              loadMainDartJs();
+            }
+          });
+
+        // If service worker doesn't succeed in a reasonable amount of time,
+        // fallback to plaint <script> tag.
+        setTimeout(() => {
+          if (!scriptLoaded) {
+            console.warn(
+              'Failed to load app from service worker. Falling back to plain <script> tag.',
+            );
+            loadMainDartJs();
+          }
+        }, 4000);
       });
+    } else {
+      // Service workers not supported. Just drop the <script> tag.
+      loadMainDartJs();
     }
   </script>
-  <script src="//cdnjs.cloudflare.com/ajax/libs/pdf.js/2.8.335/pdf.min.js"></script>
-  <script type="text/javascript">
-     pdfjsLib.GlobalWorkerOptions.workerSrc = "//cdnjs.cloudflare.com/ajax/libs/pdf.js/2.8.335/pdf.worker.min.js";
-  </script>
-  <script src="main.dart.js" type="application/javascript"></script>
 </body>
 </html>

 {
-    "name": "printing_demo",
-    "short_name": "printing_demo",
+    "name": "Flutter PDF Demo",
+    "short_name": "Flutter PDF Demo",
     "start_url": ".",
     "display": "standalone",
     "background_color": "#0175C2",
     "theme_color": "#0175C2",
-    "description": "A new Flutter project.",
+    "description": "Flutter PDF Demo.",
     "orientation": "portrait-primary",
     "prefer_related_applications": false,
     "icons": [