Add metrics for SameSite context considering redirect chain

This adds histograms and UseCounter/UKM to measure the impact of the
cookie spec change in
httpwg/http-extensions#1348, which incorporates
the redirect chain into the computation of a request's same-site or
cross-site status.

The histograms measure, on a per-cookie level, how many cookies are
affected by the change (i.e. how many cookies have their ultimate
inclusion changed by considering a cross-site redirect to make the
request cross-site) as well as the SameSite attributes of those affected
cookies.

The UseCounter/UKM measures how many pageloads have impacted cookies.

Bug: 1221316
Change-Id: I018f110466aa08e304c46f6de26fb1cc18facf33
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3024588
Reviewed-by: Steven Bingler <[email protected]>
Reviewed-by: danakj <[email protected]>
Reviewed-by: Matt Falkenhagen <[email protected]>
Reviewed-by: Robert Kaplow <[email protected]>
Commit-Queue: Lily Chen <[email protected]>
Cr-Commit-Position: refs/heads/master@{#903573}
NOKEYCHECK=True
GitOrigin-RevId: 2db3a4287cc5ebbd7b1189509380cfc5647715ef

blink/public/mojom/web_feature/web_feature.mojom

@@ -3274,6 +3274,7 @@ enum WebFeature {
   kV8URLPattern_Constructor = 3959,
   kV8URLPattern_Test_Method = 3960,
   kV8URLPattern_Exec_Method = 3961,
+  kSameSiteCookieInclusionChangedByCrossSiteRedirect = 3962,
 
   // Add new features immediately above this line. Don't change assigned
   // numbers of any item, and don't reuse removed slots.