WPT import https://crrev.com/c/998253 introduced new failures in external/wpt/background-fetch:

List of new failures:
[ Mac-mac10.12 ] external/wpt/background-fetch/interfaces.worker.html new failing tests: https://crrev.com/c/998253/4/third_party/WebKit/LayoutTests/platform/mac-mac10.12/external/wpt/background-fetch/interfaces.worker-expected.txt
[ Win ] external/wpt/background-fetch/interfaces.worker.html new failing tests: https://crrev.com/c/998253/4/third_party/WebKit/LayoutTests/platform/win/external/wpt/background-fetch/interfaces.worker-expected.txt

This import contains upstream changes from 384edc99c0e2cac89b0d0c3d405a913fb045bd20 to 4d1c1925e6c863b9365d7b8196f7b538378ffdb5:
Check inherited interfaces exist (#10285): https://github.com/w3c/web-platform-tests/commit/4d1c1925e6c863b9365d7b8196f7b538378ffdb5 [affecting this directory]
Merge pull request #10315 from kereliuk/automate-focus-02: https://github.com/w3c/web-platform-tests/commit/841f3f5a8346d6bbbe3043c1d1bc3b32aa0dabbc
AccName: Fix several expected results: https://github.com/w3c/web-platform-tests/commit/08906cbdebfc35653d9435916f43bdfa55b3c1eb
Web Animations: remove timing objects: https://github.com/w3c/web-platform-tests/commit/f6c1d7b9aafaa94ab53239634e1bbc433e32adb4
Add a runtime flag to restrict AppCache to secure contexts.: https://github.com/w3c/web-platform-tests/commit/bf17459a71ff4d1ea280bae54dd046ecf86e0628
Tests were referencing the wrong reference tests (#10328): https://github.com/w3c/web-platform-tests/commit/d725f2a5ee25de55dabfae4e9e2baec21b9a2012
added testdriver automation: https://github.com/w3c/web-platform-tests/commit/5f32ba4f5129de8d87c9111d09754820d959ae68