This fixes a canvas anti-fingerprinting gap: in Private Browsing, pixel-readback noise injection was not applied to OffscreenCanvas used inside shared workers and service workers. In Private Browsing (Advanced Privacy Protections), each ScriptExecutionContext carries a per-origin noise-injection hash salt and AdvancedPrivacyProtections flags, sourced from the document loader, and these are used to perturb pixels read back from canvas/OffscreenCanvas so the output cannot be used as a stable fingerprint. For dedicated workers the salt/flags were already plumbed via WorkerParameters to the WorkerGlobalScope, so OffscreenCanvas there got noise. But shared workers and service workers run their OffscreenCanvas code in a separate, potentially-remote Page that had neither the hash salt nor the AdvancedPrivacyProtections flags, so readback in those contexts received NO noise — letting a site fingerprint the device/OS via OffscreenCanvas from a shared/service worker, bypassing the Private Browsing protection.

The fix extends the AdvancedPrivacyProtections plumbing to those two worker types: it adds an override point (ScriptExecutionContext::advancedPrivacyProtections, implemented by Document via the top document’s loader and by workers via passed-in parameters), threads the flags through WorkerScriptLoader / WorkerInitializationData / WorkerParameters, and lets Page::setupForRemoteWorker receive the privacy protections when initializing the remote Page.

The restored invariant is that canvas/OffscreenCanvas readback noise is applied in all worker types (dedicated, shared, service) when Private Browsing protections are active. The test verifies noise injection for OffscreenCanvas in a shared worker.

A privacy/anti-fingerprinting gap in the WebContent process with no memory corruption: OffscreenCanvas readback in shared/service workers escaped Private Browsing noise injection, allowing device/OS fingerprinting that the protection is meant to prevent. The risk is tracking/deanonymization of Private Browsing users, not code execution.