Fix position: fixed support detection for Webkit

Don't support 6, 60-69, 54-59. Support everything higher than 534.

Also:
* Remove separate execution path for tests (optional argument).
* Make test case names more meaningful (include UA instead of number).

Change-Id: Ib777d244365799fd977ad07582e19f5e0b613241
Merge "Fix position: fixed support detection for Webkit"