Update Flutter web code

.metadata

@@ -1,26 +1,23 @@
 # This file tracks properties of this Flutter project.
 # Used by Flutter tool to assess capabilities and perform upgrades etc.
 #
-# This file should be version controlled.
+# This file should be version controlled and should not be manually edited.
 
 version:
-  revision: e99c9c7cd9f6c0b2f8ae6e3ebfd585239f5568f4
-  channel: stable
+  revision: "300451adae589accbece3490f4396f10bdf15e6e"
+  channel: "stable"
 
 project_type: app
 
 # Tracks metadata for the flutter migrate command
 migration:
   platforms:
     - platform: root
-      create_revision: e99c9c7cd9f6c0b2f8ae6e3ebfd585239f5568f4
-      base_revision: e99c9c7cd9f6c0b2f8ae6e3ebfd585239f5568f4
-    - platform: android
-      create_revision: e99c9c7cd9f6c0b2f8ae6e3ebfd585239f5568f4
-      base_revision: e99c9c7cd9f6c0b2f8ae6e3ebfd585239f5568f4
+      create_revision: 300451adae589accbece3490f4396f10bdf15e6e
+      base_revision: 300451adae589accbece3490f4396f10bdf15e6e
     - platform: web
-      create_revision: e99c9c7cd9f6c0b2f8ae6e3ebfd585239f5568f4
-      base_revision: e99c9c7cd9f6c0b2f8ae6e3ebfd585239f5568f4
+      create_revision: 300451adae589accbece3490f4396f10bdf15e6e
+      base_revision: 300451adae589accbece3490f4396f10bdf15e6e
 
   # User provided section
 

web/index.html

@@ -34,7 +34,7 @@
 
   <script>
     // The value below is injected by flutter build, do not touch.
-    var serviceWorkerVersion = null;
+    const serviceWorkerVersion = null;
   </script>
   <!-- This script adds the flutter initialization JS code -->
   <script src="flutter.js" defer></script>
@@ -46,11 +46,12 @@
       _flutter.loader.loadEntrypoint({
         serviceWorker: {
           serviceWorkerVersion: serviceWorkerVersion,
+        },
+        onEntrypointLoaded: function(engineInitializer) {
+          engineInitializer.initializeEngine().then(function(appRunner) {
+            appRunner.runApp();
+          });
         }
-      }).then(function(engineInitializer) {
-        return engineInitializer.initializeEngine();
-      }).then(function(appRunner) {
-        return appRunner.runApp();
       });
     });
   </script>