Track number of loaded plugins

Reviewed By: lblasa

Differential Revision: D50556872

fbshipit-source-id: 2d841360f7081074afa025d0bad8c41d7b2db16e

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

@@ -22,10 +22,11 @@ class UIPerfTracker {
     this.t0 = performance.now();
   }
 
-  track(event: UIPerfEvents) {
+  track(event: UIPerfEvents, data?: any) {
     const tx = performance.now();
     getLogger().track('performance', event, {
       time: tx - this.t0,
+      data,
     });
   }
 }