Early drafts of CSP2 contained a `reflected-xss` directive, which is little more than syntactic sugar for the `X-XSS-Protection` header. It offered no additional functionality beyond that header, just a better syntax. I shipped our implementation as part of shipping CSP2 (https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/wToP6b04zVE/imuPatGy3awJ). I should have undone that in 2015 when we dropped the directive from the CR draft. I'd like to undo it now.