1 Test that CSS stylesheets don't lose custom properties on GC when only reachable through child rules.
3 On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
6 PASS style.sheet is an instance of CSSStyleSheet
7 PASS style.sheet is null
8 FAIL rule.parentStyleSheet.foo should be 0. Threw exception TypeError: Cannot read property 'foo' of null
9 PASS successfullyParsed is true