API to report events

Summary:
Extends the WebPerformance API with ability to report events, [according to the standard](https://www.w3.org/TR/event-timing/#sec-performance-event-timing).

This is an API-only change, the actual reporting comes in a separate diff, to simplify reviewing.

Changelog: [Internal]

Reviewed By: christophpurrer

Differential Revision: D42097695

fbshipit-source-id: d8b468ffed50c1c3d889151df5e8ca644d6e1a68

Libraries/WebPerformance/NativePerformanceObserver.js

@@ -16,6 +16,8 @@ export const RawPerformanceEntryTypeValues = {
   UNDEFINED: 0,
   MARK: 1,
   MEASURE: 2,
+  EVENT: 3,
+  FIRST_INPUT: 4,
 };
 
 export type RawPerformanceEntryType = number;