[NavigationTiming] Action 56: Add object test case for Navigation Timing

I noticed the following action item from TPAC: http://www.w3.org/2010/webperf/track/actions/56 regarding Navigation Timing not having an object test case.  This test actually does already exist and is in the approved folder: http://w3c-test.org/webperf/tests/approved/navigation-timing/html5/test_performance_attributes_exist.html

Additionally, all of the other tests start with the performance namespace check before continuing.

I think it is safe to go ahead and close this one.

Thanks,
Karen