WPT import https://crrev.com/c/1157117 introduced new failures in external/wpt/css:

List of new failures:
external/wpt/css/css-pseudo/interfaces.html new failing tests: https://crrev.com/c/1157117/4/third_party/WebKit/LayoutTests/external/wpt/css/css-pseudo/interfaces-expected.txt

This import contains upstream changes from d533edcd109bf4084608515766d7744f9957633a to 54401a0a9d7a99225daf43b8e899b65744991e5f:
Update the cssom-view IDL file (#9777): https://github.com/web-platform-tests/wpt/commit/54401a0a9d7a99225daf43b8e899b65744991e5f [affecting this directory]
[wdspec] Check for correct command execution in user prompt tests.: https://github.com/web-platform-tests/wpt/commit/d6fce7bb9f5e0ce5872222b7a07b2fbbba814770
[wdspec] Check return value of dialogs in user prompt tests.: https://github.com/web-platform-tests/wpt/commit/fda2ea5e2fdd26da2fc7b77f7c317b7a74a033a2
[Gecko Bug 1476053] Optimise wpt metadata updates (#12246): https://github.com/web-platform-tests/wpt/commit/3bfba7c62a0e1b6bd6e5c075f9d0d0973b3fae72
Add UserActivation member to MessageEvent: https://github.com/web-platform-tests/wpt/commit/8a1d5c110779c525257fe2305ba7a21ae6e969e6