Test more of "await a stable state" in the resource selection algorithm

The tests target HTML r8507 and will likely need to updated soon:

https://www.w3.org/Bugs/Public/show_bug.cgi?id=24361
https://www.w3.org/Bugs/Public/show_bug.cgi?id=24707
https://www.w3.org/Bugs/Public/show_bug.cgi?id=24724