Teach URLRequest about initiator checks for First-Party-Only cookies.

net/url_request/url_request.cc

Index: net/url_request/url_request.cc
diff --git a/net/url_request/url_request.cc b/net/url_request/url_request.cc
index 4d1a871d39eec390bfaee27f446f4f34ef510ddb..7bd01e0a6c26354a3fb99370bb5027cbbe5f0c4c 100644
--- a/net/url_request/url_request.cc
+++ b/net/url_request/url_request.cc
@@ -474,6 +474,11 @@ void URLRequest::set_first_party_url_policy(
   first_party_url_policy_ = first_party_url_policy;
 }
 
+void URLRequest::set_initiator(const url::Origin& initiator) {
+  DCHECK(!is_pending_);
+  initiator_ = initiator;
+}
+
 void URLRequest::set_method(const std::string& method) {
   DCHECK(!is_pending_);
   method_ = method;