displayPerformanceMetrics example

 $this->response instanceof DownloadResponse
            && ! $this->response instanceof RedirectResponse
        ) {
            // Cache it without the performance metrics replaced             // so that we can have live speed updates along the way.             // Must be run after filters to preserve the Response headers.             $this->pageCache->make($this->request, $this->response);

            // Update the performance metrics             $body = $this->response->getBody();
            if ($body !== null) {
                $output = $this->displayPerformanceMetrics($body);
                $this->response->setBody($output);
            }

            // Save our current URI as the previous URI in the session             // for safer, more accurate use with `previous_url()` helper function.             $this->storePreviousURL(current_url(true));
        }

        unset($uri);

        // Is there a post-system event?