Something recently reminded me about the existence of USVString. According to WebIDL:

Specifications should only use USVString for APIs that perform text processing and need a string of Unicode scalar values to operate on. Most APIs that use strings should instead be using DOMString, which does not make any interpretations of the code units in the string. When in doubt, use DOMString.

I think this means we should probably use USVString for GPUShaderModuleDescriptor.code, and probably GPUProgrammableStageDescriptor.entryPoint. I'm not 100% sure whether we should use it in other places.

I did some quick reading, and my understanding is that DOMStrings which are not valid USVStrings (i.e. they have invalid surrogate pairs) cannot be converted to UTF-8. Most or all of our other DOMString inputs (labels and debug names) are fed into the GPU driver as UTF-8 at some point. So I think we cannot actually accept DOMString for those.