This is because the "if (m_context.variationFontsEnabled)" is false in the CSSPropertyFontVariationSettings block of CSSParser::parseValue().
The other CSSParserContext() constructor is being called (implicitly because of the CSSParserMode in DOMCSSNamespace::supports())
This should be fixed by https://bugs.webkit.org/show_bug.cgi?id=164251 *** This bug has been marked as a duplicate of bug 164251 ***
....which isn't going to happen. Back to "reopened"
Created attachment 293505 [details] Patch
Comment on attachment 293505 [details] Patch Attachment 293505 [details] did not pass ios-sim-ews (ios-simulator-wk2): Output: http://webkit-queues.webkit.org/results/2418091 New failing tests: fast/text/variations/css-supports-runtime-switch.html
Created attachment 293516 [details] Archive of layout-test-results from ews126 for ios-simulator-wk2 The attached test failures were seen while running run-webkit-tests on the ios-sim-ews. Bot: ews126 Port: ios-simulator-wk2 Platform: Mac OS X 10.11.6
Created attachment 293737 [details] Patch for committing
Comment on attachment 293737 [details] Patch for committing Clearing flags on attachment: 293737 Committed r208321: <http://trac.webkit.org/changeset/208321>