track onMessage performance

Summary: Tracking the time of onMessage callback

Reviewed By: passy

Differential Revision: D15536546

fbshipit-source-id: 9e93c11555a0a045ef60355ec1d0c6ca7cd49cdd

src/Client.js

@@ -112,9 +112,17 @@ export default class Client extends EventEmitter {
     const client = this;
     this.responder = {
       fireAndForget: (payload: {data: string}) =>
-        requestIdleCallback(() => client.onMessage(payload.data), {
+        requestIdleCallback(
+          () => {
+            const mark = 'onMessageCallback';
+            performance.mark();
+            client.onMessage(payload.data);
+            this.logger.trackTimeSince(mark);
+          },
+          {
             timeout: 500,
-        }),
+          },
+        ),
     };
 
     if (conn) {