Proposal: RegisteredContentScript.workers property to inject WorkerScope(s)

[hackademix]

(As discussed in #103)

Main world scripts should be able to modify JavaScript-accessible object (e.g. DOM prototypes or built-in functions) in a way that is transparent and cannot be subverted by page scripts., e.g. to modify or intercept the behavior of built-in objects for additional security, privacy and/or anti-fingerprinting reasons.

This requires them to be injected and running before site scripts in any scope, including WorkerScope(s) (workers, shared workers and service workers), otherwise these scope can be use to circumvent the main browsing context modifications.

Therefore, in addition to the RegisteredContentScript properties already specified, we propose to add:

• workers Optional
  boolean, default false: if true, all the Worker, SharedWorker and ServiceWorker scopes which are associated to the browsing contexts matched this RegisteredContentScript filters will be injected as well.