[FedCM] Send SameSite=Lax cookies, in addition to None

See discussion in w3c-fedid/FedCM#587

This is behind the FedCmSameSiteLax flag for now.

Bug: 350944661
Change-Id: I3e5fe99b98560f680217cd3326ff66d290a5290f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5675433
Reviewed-by: Yi Gu <yigu@chromium.org>
Commit-Queue: Christian Biesinger <cbiesinger@chromium.org>
Reviewed-by: Charlie Reis <creis@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1325570}

fedcm/support/accounts_check_same_site_strict.py

@@ -7,6 +7,7 @@ def main(request, response):
     return request_error
   if request.cookies.get(b"same_site_strict") == b"1":
     return (546, [], "Should not send SameSite=Strict cookies")
+  # TODO(crbug.com/350944661): We want to send these cookies.
   if request.cookies.get(b"same_site_lax") == b"1":
     return (547, [], "Should not send SameSite=Lax cookies")
   if request.headers.get(b"Sec-Fetch-Site") != b"cross-site":

fedcm/support/token_check_same_site_strict.py

@@ -7,6 +7,7 @@ def main(request, response):
     return request_error
   if request.cookies.get(b"same_site_strict") == b"1":
     return (546, [], "Should not send SameSite=Strict cookies")
+  # TODO(crbug.com/350944661): We want to send these cookies.
   if request.cookies.get(b"same_site_lax") == b"1":
     return (547, [], "Should not send SameSite=Lax cookies")