WPT import https://crrev.com/c/1159331 introduced new failures in external/wpt/css/vendor-imports/mozilla/mozilla-central-reftests/flexbox:

List of new failures:
[ Linux Mac Win7 ] external/wpt/css/vendor-imports/mozilla/mozilla-central-reftests/flexbox/flexbox-column-row-gap-004.html [ Failure ]

This import contains upstream changes from 8e668a6b63e5dbb68304c182fdc1f7b4e6edaf96 to 0c3bed38df6d9dcd1441873728fb5c1bb59c92df:
Add tests for self.queueMicrotask(): https://github.com/web-platform-tests/wpt/commit/0c3bed38df6d9dcd1441873728fb5c1bb59c92df
[Gecko Bug 1479290] Reduce memory usage of wpt-update (#12247): https://github.com/web-platform-tests/wpt/commit/6a894939f7522f23429fca84b4d184571818504e
HTML: Capture event handler removal errors correctly: https://github.com/web-platform-tests/wpt/commit/74938e820dbb52a9fa50b6a2ff906c7187e547d5
servodriver: Correct reference to server configuration.: https://github.com/web-platform-tests/wpt/commit/02400e56c310cbac2b331848f3bb01855c6ffc67
servodriver: Use config property instead of kwarg for browser kwargs.: https://github.com/web-platform-tests/wpt/commit/d769d0a84a3e6d941775fb2479f6457e9ddb8d36
Sync Mozilla tests as of https://hg.mozilla.org/mozilla-central/rev/af6a7edf0069549543f2fba6a8ee3ea251b20829 . (#12258): https://github.com/web-platform-tests/wpt/commit/c0ef9d68c8c5ceb8802a5a2ede1c3c5b3ecbcae8 [affecting this directory]
[wdspec] Remove createFile fixture and file upload tests for multiple folders.: https://github.com/web-platform-tests/wpt/commit/305b5ab50e771a70c65070eb9dcbbd01595d6dfb
Update the dom IDL file (#9779): https://github.com/web-platform-tests/wpt/commit/04e4fdae473c5f969b54404f18c586f54039363b
Fold "Unscopable handled correctly" tests into the attribute/operation tests (#12211): https://github.com/web-platform-tests/wpt/commit/2f8b11a39d4da8d729903b1b30557a875d5bf76a