Uses Azure App Insights to track that a call to the Graph has occurred (and the duration).

SPFx_AddTiming_GraphCall.ts

// start timer here..
      this._startTime = new Date();

      this.props.context.graphHttpClient.get(`v1.0/groups/${groupId}/events`, GraphHttpClient.configurations.v1).then((response: HttpClientResponse) => {
        if (response.ok) {
          return response.json();
        } else {
          console.warn(response.statusText);
        }
      }).then((result: any) => {
        // end timer here and log..
        this._endTime = new Date();
        var timeTaken: number = this._endTime.valueOf() - this._startTime.valueOf();
        console.log(`componentWillMount: Took ${ timeTaken } ms to call Graph.`);

        AppInsights.trackEvent("Fetch calendar events",
          {},
          { timeTaken: timeTaken }
        );

        console.log("componentWillMount: Fetched result.value.length = " + result.value.length);
        this._processing = false;

        // process events..
        let appointments: string = '';
        for (var i:number = 0; i < result.value.length; i++) {
          var item: any = result.value[i];
          var eventItem: IEventItem = {
            subject: item.subject,
            startTime: new Date().toString(),
            endTime: new Date().toString(),
            thumbnail: ""
          };

          fetchedEvents.push(eventItem);
          appointments += item.subject + "|";
        }