Currently renderer-side objects around EmbeddedWorkerInstanceClientImpl owned by a reference cycle like the following:
EmbeddedWorkerInstanceClientImpl -(owns)-> WorkerWrapper -(owns)-> WebEmbeddedWorkerInstance -(owns)-> ServiceWorkerContextClient -(owns)-> EmbeddedWorkerInstanceClientImpl

It could be simplified if the browser-side has the ownership of EWInstanceClientImpl, or EWInstanceClientImpl owns itself.