Fix the invalid method name in Webrtc tests

Bug: 1102606
Change-Id: I1f26284306d832fa2fe1ad6578bca6c6eb193843
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2284005Reviewed-by: Mirko Bonadei <mbonadei@chromium.org>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Lahiru Ginnaliya Gamathige <glahiru@google.com>
Cr-Commit-Position: refs/heads/master@{#785854}

tools/perf/page_sets/webrtc_cases/multiple-peerconnections.js

@@ -17,7 +17,7 @@ var cpuOveruseDetectionCheckbox = $('cpuoveruse-detection');
 startTestButton.onclick = startTest;
 
 function logError(err) {
-  console.err(err);
+  console.error(err);
 }
 
 function addNewVideoElement() {