SameSite: Strict/Lax behavior.

This patch brings our "SameSite" implementation into line with
https://tools.ietf.org/html/draft-west-first-party-cookies-06 by teaching
CookieOptions about strict and lax request modes, and teaching URLRequestHttpJob
about the registrable-domain behaviors of both.

BUG=459154
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_site_isolation

Review URL: https://codereview.chromium.org/1783813002

Cr-Commit-Position: refs/heads/master@{#382277}
25 files changed