WPT import https://crrev.com/c/1108384 introduced new failures in external/wpt/background-fetch:

List of new failures:
external/wpt/background-fetch/interfaces.https.any.worker.html new failing tests: https://crrev.com/c/1108384/4/third_party/WebKit/LayoutTests/external/wpt/background-fetch/interfaces.https.any.worker-expected.txt
external/wpt/background-fetch/interfaces.https.any.html new failing tests: https://crrev.com/c/1108384/4/third_party/WebKit/LayoutTests/external/wpt/background-fetch/interfaces.https.any-expected.txt

This import contains upstream changes from f681986a5885db4ed90622de47cd8ba269ba287e to b71b2c58623ee15f0918b7388bf9cd11976b4b1b:
[Mojo Blob URLs] Make clicking an <a target="blank_"> with a blob URL work correctly.: https://github.com/web-platform-tests/wpt/commit/b71b2c58623ee15f0918b7388bf9cd11976b4b1b
Update the secure-contexts IDL file and test (#9848): https://github.com/web-platform-tests/wpt/commit/08ffa82f0c85c931ed162362c39f2e7cf0d19612
HTML: Split up parse-a-sizes-attribute.html: https://github.com/web-platform-tests/wpt/commit/b61072d88ae05ae584f28bac9ea361e87e752f59
Update the background-fetch IDL file (#9760): https://github.com/web-platform-tests/wpt/commit/187c07cdb2ac5cc8b3decb1071850f047d415c81 [affecting this directory]