onContextInvalidated doesn't work in Safari

[fregante]

• chrome.runtime.id is still set after context invalidation
• sendMessage fails silently (the promise resolves, the callback isn't called)
• storage.local.get() returns Promise<undefined>
• storage.local.set() throws asynchronously with Error: Extension API is being called from a webpage that does not have extension content.

So far the best way to detect context invalidation seems to be:

return isSuccessful(chrome.storage.local.set({isContextInvalidated: undefined}))