media: Restrict ProtectedMediaIdentifier permission to secure origins

Currently EME is restricted to secure origins (see BUG). However, it's
possible that the renderer process is compromised and bypasses this
restriction. This CL restricts the ProtectedMediaIdentifier permission
to secure origin as well to add another layer of protection.

Origins whitelisted by the --unsafely-treat-insecure-origin-as-secure
flag will always be treated as "secure", and as such will not be
affected by this change.

BUG=672605

Review-Url: https://codereview.chromium.org/2859293003
Cr-Commit-Position: refs/heads/master@{#469866}
1 file changed