Copied from the falken@'s comment on the spec issue:

> It turned out Chrome is the only browser with immediate plans to implement module service workers.
> 
> There was rough consensus that throwing on dynamic imports for now is the safe thing to do, with room to change later as we get real usage of module service workers and understand the problem more.
> 
> Todo:
> Spec that static module imports are installed
> Spec that dynamic module imports throw
> Add tests.

For implementation, we can do the same thing with WorkletModulatorImpl::IsDynamicImportForbidden().