Add ui performance tracker

Reviewed By: lblasa

Differential Revision: D50121106

fbshipit-source-id: 54650de65e11c80ea776eafd85cdd5b7749a4fd4

desktop/flipper-ui-core/src/utils/UIPerfTracker.tsx

@@ -0,0 +1,29 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+import {getLogger} from 'flipper-common';
+
+type UIPerfEvents = 'ui-perf-everything-finally-loaded-jeeeez';
+
+class UIPerfTracker {
+  private t0!: number;
+
+  _init() {
+    this.t0 = performance.now();
+  }
+
+  track(event: UIPerfEvents) {
+    const tx = performance.now();
+    getLogger().track('performance', event, {
+      time: tx - this.t0,
+    });
+  }
+}
+
+export const uiPerfTracker = new UIPerfTracker();