sendToPage property
Sends a message back to the page, when a page is reachable.
Wired by the runtime: the compiled worker bundle sets it to post to the
owning page (or to open pages via clients.postMessage in the Service
Worker context); the page sets it for the in-page fallback path. Dispatcher
code can call this at any time; the page observes the message on
WorkmanagerWeb.workerMessages.
Implementation
PageMessageSender? sendToPage;