WPT import https://crrev.com/c/1000000 introduced new failures in external/wpt/background-fetch:

List of new failures:
external/wpt/background-fetch/interfaces.worker.html new failing tests: https://crrev.com/c/1000000/4/third_party/WebKit/LayoutTests/external/wpt/background-fetch/interfaces.worker-expected.txt

This import contains upstream changes from 0cddb6844a669459eb30f0bcf175e16e38af2a54 to 6e68c444ed00317ee7035fd2e1e144eb4a6a6091:
Improve idlharness error message for exposure test (#10336): https://github.com/w3c/web-platform-tests/commit/6e68c444ed00317ee7035fd2e1e144eb4a6a6091
Cookie Store: Tentatively deflake special names test: https://github.com/w3c/web-platform-tests/commit/a4c17db5364ca97ffa9bb76f9c8e6e155ecd3ddb
Move AudioNode tests to WPT: https://github.com/w3c/web-platform-tests/commit/68b07988d40f8a0250675fd0de3c6ae96921608e
Update mozrunner from 6.14 to 6.15 (#10346): https://github.com/w3c/web-platform-tests/commit/ea9348739755aa9bac698f8032ec73d02bc2174a
Cookie Store: rework tests for 'expires' option: https://github.com/w3c/web-platform-tests/commit/8b9501b721963f2b3886f25e20f17a2afe6bc381
Update ReadableStream to latest standard version: https://github.com/w3c/web-platform-tests/commit/8314b7b5ae86ebf5bc435558ae5b0af32b1d7756
Fix the |name| of PerformanceNavigationTiming: https://github.com/w3c/web-platform-tests/commit/a0091fbff26091db1fd4b6ca07d9512edf7e6a95
Make BlueTooth/USB requestDevice non-consuming.: https://github.com/w3c/web-platform-tests/commit/6ba01ea2ffbafbb329352628b244815654b38156