Add feature flag for schemeful same-site

This flag will control if the same-site calculation will take the scheme
of the site-for-cookies and the request/response url into account when
determining same-site-ness or cross-site-ness.

Bug: 1030938
Change-Id: I206accc412cc8e2f4d3c65b8d3ab248bb3fa66bd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2062636Reviewed-by: Maksim Orlovich <morlovich@chromium.org>
Commit-Queue: Steven Bingler <bingler@chromium.org>
Cr-Commit-Position: refs/heads/master@{#743377}

net/base/features.cc

@@ -114,5 +114,8 @@ const base::Feature kTurnOffStreamingMediaCaching{
 const base::Feature kLegacyTLSEnforced{"LegacyTLSEnforced",
                                        base::FEATURE_DISABLED_BY_DEFAULT};
 
+const base::Feature kSchemefulSameSite{"SchemefulSameSite",
+                                       base::FEATURE_DISABLED_BY_DEFAULT};
+
 }  // namespace features
 }  // namespace net

net/base/features.h

@@ -162,6 +162,10 @@ NET_EXPORT extern const base::Feature kTurnOffStreamingMediaCaching;
 // warning for these pages.
 NET_EXPORT extern const base::Feature kLegacyTLSEnforced;
 
+// When enabled this feature will cause same-site calculations to take into
+// account the scheme of the site-for-cookies and the request/response url.
+NET_EXPORT extern const base::Feature kSchemefulSameSite;
+
 }  // namespace features
 }  // namespace net