JS side implementation of PerformanceObserver API

Summary:
[Changelog][Internal]

This adds module specs for the native part of PerformanceObserver, as well as the interaction logic vs the NativePerformanceObserver API.

See https://fb.quip.com/MdqgAk1Eb2dV for more detail.

Reviewed By: rubennorte

Differential Revision: D40897006

fbshipit-source-id: 77475f21dad9ee9dbe15df5a989eb08d314e6db2

Libraries/NativeModules/specs/NativePerformanceObserverCxx.js

@@ -0,0 +1,44 @@
+/**
+ * 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.
+ *
+ * @flow strict
+ * @format
+ */
+
+import type {TurboModule} from '../../TurboModule/RCTExport';
+
+import * as TurboModuleRegistry from '../../TurboModule/TurboModuleRegistry';
+
+export type RawTimeStamp = number;
+
+export const RawPerformanceEntryTypeValues = {
+  UNDEFINED: 0,
+};
+
+export type RawPerformanceEntryType = number;
+
+export type RawPerformanceEntry = $ReadOnly<{
+  name: string,
+  entryType: RawPerformanceEntryType,
+  startTime: RawTimeStamp,
+  duration: number,
+
+  // For "event" entries only:
+  processingStart?: RawTimeStamp,
+  processingEnd?: RawTimeStamp,
+  interactionId?: RawTimeStamp,
+}>;
+
+export type RawPerformanceEntryList = $ReadOnlyArray<RawPerformanceEntry>;
+
+export interface Spec extends TurboModule {
+  +startReporting: (entryType: string) => void;
+  +stopReporting: (entryType: string) => void;
+  +getPendingEntries: () => RawPerformanceEntryList;
+  +setOnPerformanceEntryCallback: (callback?: () => void) => void;
+}
+
+export default (TurboModuleRegistry.get<Spec>('PerformanceObserver'): ?Spec);