[Breaking change] Support SameSite in Cookies.

[sun-jiao]

Related pull request:
github
googlesource

1. The intended change in behavior: Add enum type SameSite (link) and public filed sameSite in abstract class Cookie (link) and its default implementation _Cookie (link).
2. The justification/rationale for making the change: This artribute is important for CORS requests, for example, accessing dart backend in Flutter Web. Bacause they runs on different port, browsers don't allow Flutter Web to use cookies of dart backend.
3. The expected impact of this change: all classes implement Cookie must override the filed sameSite.
4. Clear steps for mitigating the change: We can release this change in the beta and dev channels first, so developers can make changes in advance. By the time these changes appeared in the stable channel, developers will have overridden sameSite in their implementation, so their projects will not break.

[a-siva]

/cc @brianquinlan

[natebosch]

3. all classes implement Cookie must override the filed sameSite.

@brianquinlan - do we have an estimate of internal and external usage of this pattern?

[brianquinlan]

@natebosch

Known places that implement Cookie

• The archived project http_io
• One place in Google Ads where Cookie is implemented as part of a fake

[itsjustkevin]

@vsmenon @grouma @Hixie breaking change request!

@brianquinlan and @sun-jiao thank you for bringing this to my attention.

[grouma]

One place in Google Ads where Cookie is implemented as part of a fake

I'm seeing a couple more locations, including some outside Ads. Overall it is < 10 and they all seem to be testing related. Should be a fairly straightforward change.

[mit-mit]

This breaking change SGTM. @vsmenon @grouma @Hixie can you approve too?

[Hixie]

fine by me

[grouma]

SGTM.

[mit-mit]

@itsjustkevin can we consider this approved?

[itsjustkevin]

Calling this approved, @vsmenon please chime in if you disagree.

[sun-jiao]

Merged.

[shilangyu]

Any reason why SameSite is a class instead of an enum?