SameSite: Implement 'Strict'/'Lax' attribute parsing.

net/cookies/cookie_constants.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_COOKIES_COOKIE_CONSTANTS_H_
 #define NET_COOKIES_COOKIE_CONSTANTS_H_
 
 #include <string>
 
 #include "net/base/net_export.h"
 
 namespace net {
 
 enum CookiePriority {
   COOKIE_PRIORITY_LOW     = 0,
   COOKIE_PRIORITY_MEDIUM  = 1,
   COOKIE_PRIORITY_HIGH    = 2,
   COOKIE_PRIORITY_DEFAULT = COOKIE_PRIORITY_MEDIUM
 };
 
+enum class CookieSameSite {
+  NO_RESTRICTION = 0,
+  LAX_MODE = 1,
+  STRICT_MODE = 2,
+  DEFAULT_MODE = NO_RESTRICTION
+};
+
 // Returns the Set-Cookie header priority token corresponding to |priority|.
-NET_EXPORT const std::string CookiePriorityToString(CookiePriority priority);
+//
+// TODO(mkwst): Remove this once its callsites are refactored.
+NET_EXPORT std::string CookiePriorityToString(CookiePriority priority);
 
 // Converts the Set-Cookie header priority token |priority| to a CookiePriority.
 // Defaults to COOKIE_PRIORITY_DEFAULT for empty or unrecognized strings.
 NET_EXPORT CookiePriority StringToCookiePriority(const std::string& priority);
 
+// Converst the Set-Cookie header SameSite token |same_site| to a
+// CookieSameSite. Defaults to CookieSameSite::DEFAULT_MODE for empty or
+// unrecognized strings.
+NET_EXPORT CookieSameSite StringToCookieSameSite(const std::string& same_site);
+
 }  // namespace net
 
 #endif  // NET_COOKIES_COOKIE_CONSTANTS_H_