Web updates

HTML 78741b7b5471

Integrate Feature Policy concepts into HTML This commit introduces the feature policy for Document objects, adds the 'allow' attribute to iframe elements, and reframes 'allowfullscreen', 'allowpaymentrequest' and 'allowusermedia' in terms of feature policy. Document allow* flags are removed, as they are no longer referenced. The 'allowed to use' algorithm is also updated to call into the feature policy 'Is feature enabled' algorithm, and rewritten to take a policy- controlled feature as an argument rather than an attribute, so that other specs can also use it to control other features. Tests: - - - -

Ian Clelland