Delegate cache control from Flutter to browser (#3289)

(cherry picked from commit 9c3954a73803a0f1921926f86b9761156430dc2f)

web/index.html

@@ -104,15 +104,33 @@
     
     loadLanguageResources().finally(initialTmailApp);
 
-    _flutter.loader.load({
-      serviceWorkerSettings: {
-        serviceWorkerVersion: {{flutter_service_worker_version}},
-      },
-      onEntrypointLoaded: async function(engineInitializer) {
-        const appRunner = await engineInitializer.initializeEngine();
-        await appRunner.runApp();
-      }
-    });
+    if ('serviceWorker' in navigator) {
+      navigator
+        .serviceWorker
+        .getRegistrations()
+        .then(async function(registrations) {
+          try {
+            await Promise.all(registrations.map(function(registration) {
+              return registration.unregister();
+            }));
+          } catch (error) {
+            console.log('[Twake Mail] Error unregistering service worker: ', error);
+          }
+          _flutter.loader.load({
+            onEntrypointLoaded: async function(engineInitializer) {
+              const appRunner = await engineInitializer.initializeEngine();
+              await appRunner.runApp();
+            }
+          });
+        });
+    } else {
+      _flutter.loader.load({
+        onEntrypointLoaded: async function(engineInitializer) {
+          const appRunner = await engineInitializer.initializeEngine();
+          await appRunner.runApp();
+        }
+      });
+    }
   </script>
   <script src="https://unpkg.com/pica/dist/pica.min.js" ></script> 
 </body>