This CL replaces e-mail with AccountId on user selection screen.

components/signin/core/account_id/account_id.cc

 // Copyright 2015 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.
 
 #include "components/signin/core/account_id/account_id.h"
 
 #include <functional>
 
+#include "base/json/json_reader.h"
+#include "base/json/json_writer.h"
 #include "base/memory/singleton.h"
+#include "base/values.h"
 #include "google_apis/gaia/gaia_auth_util.h"
 
 namespace {
 
 // Known account types.
 const char kGoogle[] = "google";
 
+// Serialization keys
+const char kGaiaIdKey[] = "gaia_id";
+const char kEmailKey[] = "email";
+
 struct GoogleStringSingleton {
   GoogleStringSingleton() : google(kGoogle) {}
 
   static GoogleStringSingleton* GetInstance() {
     return base::Singleton<GoogleStringSingleton>::get();
   }
 
   const std::string google;
 };
 
@@ skipping 81 matching lines @@
   return AccountId(gaia_id, std::string() /* email */);
 }
 
 // static
 AccountId AccountId::FromUserEmailGaiaId(const std::string& email,
                                          const std::string& gaia_id) {
   DCHECK(!(email.empty() && gaia_id.empty()));
   return AccountId(gaia_id, email);
 }
 
+std::string AccountId::Serialize() const {
+  base::DictionaryValue value;
+  value.SetString(kGaiaIdKey, gaia_id_);
+  value.SetString(kEmailKey, user_email_);
+
+  std::string serialized;
+  base::JSONWriter::Write(value, &serialized);
+  return serialized;
+}
+
+// static
+bool AccountId::Deserialize(const std::string& serialized,
+                            AccountId* account_id) {
+  base::JSONReader reader;
+  scoped_ptr<const base::Value> value(reader.Read(serialized));
+  const base::DictionaryValue* dictionary_value = NULL;
+
+  if (!value || !value->GetAsDictionary(&dictionary_value))
+    return false;
+
+  std::string gaia_id;
+  std::string user_email;
+
+  const bool found_gaia_id = dictionary_value->GetString(kGaiaIdKey, &gaia_id);
+  const bool found_user_email =
+      dictionary_value->GetString(kEmailKey, &user_email);
+
+  if (!found_gaia_id)
+    LOG(ERROR) << "gaia_id is not found in '" << serialized << "'";
+
+  if (!found_user_email)
+    LOG(ERROR) << "user_email is not found in '" << serialized << "'";
+
+  if (!found_gaia_id && !found_user_email)
+    return false;
+
+  *account_id = FromUserEmailGaiaId(user_email, gaia_id);
+
+  return true;
+}
+
 const AccountId& EmptyAccountId() {
   return AccountId::EmptyAccountId::GetInstance()->user_id;
 }
 
 namespace BASE_HASH_NAMESPACE {
 
 std::size_t hash<AccountId>::operator()(const AccountId& user_id) const {
   return hash<std::string>()(user_id.GetUserEmail());
 }
 
 }  // namespace BASE_HASH_NAMESPAC