Add observer type to Perf event

Summary: While looking at the event stream it is useful to know which observer type fired it

Reviewed By: lblasa

Differential Revision: D39430756

fbshipit-source-id: bc52f085a5497692f8076b12a9c015cc33a19d1e

desktop/plugins/public/ui-debugger/index.tsx

@@ -12,6 +12,7 @@ import {Id, UINode} from './types';
 
 export type PerfStatsEvent = {
   txId: number;
+  observerType: string;
   start: number;
   traversalComplete: number;
   serializationComplete: number;