Add a SetCanonicalCookie method for CookieMonster.

net/cookies/canonical_cookie.cc

Index: net/cookies/canonical_cookie.cc
diff --git a/net/cookies/canonical_cookie.cc b/net/cookies/canonical_cookie.cc
index 11f9e0a1b74541d06c218053c8d15404032872aa..2ee2cf456187ded7c8af7db934d80cb4e5e7dbc6 100644
--- a/net/cookies/canonical_cookie.cc
+++ b/net/cookies/canonical_cookie.cc
@@ -226,6 +226,7 @@ std::unique_ptr<CanonicalCookie> CanonicalCookie::Create(
   if (options.has_server_time())
     server_time = options.server_time();
 
+  DCHECK(!creation_time.is_null());
   Time cookie_expires = CanonicalCookie::CanonExpiration(parsed_cookie,
                                                          creation_time,
                                                          server_time);
@@ -444,6 +445,11 @@ bool CanonicalCookie::IsCanonical() const {
   return true;
 }
 
+void CanonicalCookie::SetCreationDate(base::Time new_creation_date) {
+  DCHECK(CreationDate().is_null());
+  creation_date_ = new_creation_date;
+}
+
 // static
 CanonicalCookie::CookiePrefix CanonicalCookie::GetCookiePrefix(
     const std::string& name) {