Messages between windows now prove who sent them

A quieter fix, but a real one, all on your device. When two windows or an embedded frame talk to each other, the message now carries the true address of who sent it, so the receiving side can check it came from a source it trusts before acting on it - the check that keeps a hostile page from impersonating a trusted one. And when a page sends such a message addressed to a specific site, the browser now holds that promise: if the window it lands in belongs to a different site the message is withheld, so a page can no longer hand a private token to whatever happens to be sitting in the frame. The security architecture aspect moves 64 to 65; the overall platform score stays at 70.