Add UI for INSECURE_PRIVATE_NETWORK site setting (default disabled)

[uazo]

Intel® Driver & Support Assistant seems to be able to access to localhost, but is it correct that the user is not notified?

check:

• https://bugs.chromium.org/p/chromium/issues/detail?id=1382068
• https://bugs.chromium.org/p/chromium/issues/detail?id=986744

[uazo]

temporary workaround: set chrome://flags/#private-network-access-respect-preflight-results

[uazo]

check what are they for ContentSettingsType::INSECURE_PRIVATE_NETWORK and ContentSettingsType::PRIVATE_NETWORK_GUARD

Issue 1338439: Prototyping permission prompt for private network access
https://bugs.chromium.org/p/chromium/issues/detail?id=1338439

idl change third_party/blink/renderer/core/fetch/request.idl

[uazo]

so INSECURE_PRIVATE_NETWORK and PRIVATE_NETWORK_GUARD are two different things.
the first is a policy-based on/off and allows access or denial to any local resource for all sites, unless InsecurePrivateNetworkRequestsAllowedForUrls is set.
the second one is more interesting but is a work in progress and allows the choice between which resources the website can access.
the first one is stable, but it would lack the ui and especially the prompt to the user

[uazo]

so, the site setting only works in Allow mode and is not active in workers.
This is unfortunate because it does not allow me to open a bug in chromium....
What's more, I noticed that the check is done only after the connection to the endpoint, so through a timing check it would still be possible to derive whether a port on a local address turns out to be open or not.
However, the modification seems feasible.

[uazo]

wip patch https://gist.github.com/uazo/e61cf8d777f4111c059466d6c6184972
temporarily suspended for rebase on v112

[uazo]

check PageSpecificContentSettings::MaybeNotifySiteDataObservers() whether it is possible to show info to the user via the ui

[uazo]

check LocalNetworkAccessChecker::CheckInternal

[uazo]

Localhost access permission in brave

[uazo]

Intent to Prototype: Private Network Access restrictions for automotive
http://groups.google.com/a/chromium.org/group/blink-dev/t/30ed8798a6857bc7
https://docs.google.com/document/d/1FYPIeP90MQ_pQ6UAo0mCB3g2Z_AynfPWHbDnHIST6VI/edit

[uazo]

new flag in v117: kPrivateNetworkAccessForWorkers kPrivateNetworkAccessForIframesWarningOnly
see FeatureStateForContext in content/browser/renderer_host/private_network_access_util.cc