Test for compliance with W3C spec

This patch makes the logging of Navigation Timing measurements conditional on
the browser passing a short self-test which verifies that the ordering of
Navigation Timing values is consistent with the spec.

The tests were derived from
<http://w3c-test.org/web-platform-tests/master/navigation-timing/test_timing_attributes_order.html>

Change-Id: Ib2f47ced37e85d92ec4be5e84861799692c7bdd5