Tests event listener breakpoints on XHRs.
Set timer for test function.
Captured call stacks in no particular order:
Call stack:
0) downloadEnd (event-listener-breakpoints-xhr.js:26)
Event target: XMLHttpRequest
Call stack:
0) downloadProgress (event-listener-breakpoints-xhr.js:34)
Event target: XMLHttpRequest
Call stack:
0) loadCallback (event-listener-breakpoints-xhr.js:42)
Event target: XMLHttpRequest
Call stack:
0) uploadEnd (event-listener-breakpoints-xhr.js:30)
Event target: XMLHttpRequestUpload
Call stack:
0) uploadProgress (event-listener-breakpoints-xhr.js:38)
Event target: XMLHttpRequestUpload
Call stack:
0) xhr.onreadystatechange (event-listener-breakpoints-xhr.js:22)
1) sendXHR (event-listener-breakpoints-xhr.js:51)
2) testFunction (event-listener-breakpoints-xhr.js:14)
Event target: XMLHttpRequest