Following https://chromium.googlesource.com/chromium/src/+/5bc093f718e75a916497b04bc379d4404021b55c the window and worker (including service worker) tests for global interfaces (i.e. what API we expose to the web) is done through a common library:

LayoutTests/resources/global-interface-listing.js

... which is used by specific tests in LayoutTests/webexposed/ and LayoutTests/http/tests/serviceworker/webexposed/ 

Worklets use their own copy of this script:

LayoutTests/http/tests/worklet/webexposed/resources/global-interface-listing-worklet.js

We should unify these. Since Worklets will be dependent on ES6 modules, the script should probably become a module, which means we need to wait (?) until we have general module support.