Async Cookies: Implement sameSite attribute.

This CL modifies RestrictedCookieManager to allow renderers to set the
SameSite and Priority CanonicalCookie attributes. Renderers must be
allowed to set the SameSite and Priority attributes so that
RestrictedCookieManager can be used to implement the document.cookie
setter.

Bug: 856364, 729800
Cq-Include-Trybots: luci.chromium.try:linux_mojo
Change-Id: Ic0a520bc6c02c259ef22175c9eb161086fa18782
Reviewed-on: https://chromium-review.googlesource.com/1115586
Commit-Queue: Victor Costan <pwnall@chromium.org>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Reviewed-by: Joshua Bell <jsbell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#570976}
7 files changed