ChromeOS cryptohome should be able to use gaia id as user identifier.

components/user_manager/known_user.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/user_manager/known_user.h"
 
 #include <stddef.h>
 
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 238 matching lines @@
   if (!gaia_id.empty() && GetStringPref(AccountId::FromGaiaId(gaia_id),
                                         kCanonicalEmail, &stored_email)) {
     return AccountId::FromUserEmailGaiaId(stored_email, gaia_id);
   }
 
   return (gaia_id.empty()
               ? AccountId::FromUserEmail(user_email)
               : AccountId::FromUserEmailGaiaId(user_email, gaia_id));
 }
 
+std::vector<AccountId> GetKnownAccountIds() {
+  std::vector<AccountId> result;
+  PrefService* local_state = GetLocalState();
+
+  // Local State may not be initialized in tests.
+  if (!local_state)
+    return result;
+
+  const base::ListValue* known_users = local_state->GetList(kKnownUsers);
+  for (size_t i = 0; i < known_users->GetSize(); ++i) {
+    const base::DictionaryValue* element = nullptr;
+    if (known_users->GetDictionary(i, &element)) {
+      std::string email;
+      std::string gaia_id;
+      const bool has_email = element->GetString(kCanonicalEmail, &email);
+      const bool has_gaia_id = element->GetString(kGAIAIdKey, &gaia_id);
+      if (has_email || has_gaia_id) {
+        result.push_back(AccountId::FromUserEmailGaiaId(email, gaia_id));
+      }
+    }
+  }
+  return result;
+}
+
+AccountId MayBeDeserializeAccountId(
+    const std::string& maybe_serialized_account_id) {
+  AccountId result(EmptyAccountId());
+
+  if (AccountId::Deserialize(maybe_serialized_account_id, &result))
+    return result;
+
+  return GetAccountId(maybe_serialized_account_id, std::string() /* gaia_id */);
+}
+
 bool GetGaiaIdMigrationStatus(const AccountId& account_id,
                               const std::string& subsystem) {
   bool migrated = false;
 
   if (GetBooleanPref(account_id,
                      std::string(kGaiaIdMigration) + "." + subsystem,
                      &migrated)) {
     return migrated;
   }
 
@@ skipping 80 matching lines @@
     }
   }
 }
 
 void RegisterPrefs(PrefRegistrySimple* registry) {
   registry->RegisterListPref(kKnownUsers);
 }
 
 }  // namespace known_user
 }  // namespace user_manager