Permission request for iframe

[danqdinh]

Current condition:

• handle.queryPermission works in any context
• handle.requestPermission works in iframe with the same host name with outer window
• Doesn't work in iframe with different host name with outer window: DOMException: Not allowed to request permissions in this context.

My service, maybe other services too, run in iframe and it needs to access files. Is it possible to lax out, loosen the security about this? coz user has to make a user activation action anyway, so it's acceptable security.

[Thomas Steiner]

Duplicate of #245.