Some SVG tests started failing 100% on Windows after r188647

[Tim Horton]

https://webkit-test-results.webkit.org/dashboards/flakiness_dashboard.html#showAllRuns=true&tests=imported%2Fmozilla%2Fsvg%2Fsvg-effects-area-unzoomed.xhtml
https://webkit-test-results.webkit.org/dashboards/flakiness_dashboard.html#showAllRuns=true&tests=imported%2Fmozilla%2Fsvg%2Fsvg-effects-area-zoomed-in.xhtml
https://webkit-test-results.webkit.org/dashboards/flakiness_dashboard.html#showAllRuns=true&tests=imported%2Fmozilla%2Fsvg%2Fsvg-effects-area-zoomed-out.xhtml

etc.

all regressed in https://trac.webkit.org/changeset/188647

It seems likely that this is because the test depends on the CSS filter: property mapping to the SVG property, and now that we've unprefixed the real filter: property this is somehow broken? But I'm not really sure.

[Tim Horton]

Dean, will you have a chance to look at this? I will probably mark them as failing, but this seems potentially like a bigger problem.