Fixing issue with XHR request.
Fixing issue with XHR request.

Synchronous XHRs are deprecated. Switching to async XHR.
https://xhr.spec.whatwg.org/#the-open()-method

Change-Id: I274c006b537e1ecbe55e5e947e39c0c6895609d3

shaka-project/eme_logger,shaka-project/eme_logger