Improve cold start performance

ts/util/incrementMessageCounter.ts

@@ -0,0 +1,23 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { debounce } from 'lodash';
+
+export function incrementMessageCounter(): number {
+  if (!window.receivedAtCounter) {
+    window.receivedAtCounter =
+      Number(localStorage.getItem('lastReceivedAtCounter')) || Date.now();
+  }
+
+  window.receivedAtCounter += 1;
+  debouncedUpdateLastReceivedAt();
+
+  return window.receivedAtCounter;
+}
+
+const debouncedUpdateLastReceivedAt = debounce(() => {
+  localStorage.setItem(
+    'lastReceivedAtCounter',
+    String(window.receivedAtCounter)
+  );
+}, 500);