We should use UserID object to identify users instead of username.

chrome/browser/chromeos/login/easy_unlock/easy_unlock_tpm_key_manager.cc

Index: chrome/browser/chromeos/login/easy_unlock/easy_unlock_tpm_key_manager.cc
diff --git a/chrome/browser/chromeos/login/easy_unlock/easy_unlock_tpm_key_manager.cc b/chrome/browser/chromeos/login/easy_unlock/easy_unlock_tpm_key_manager.cc
index cb389ed55e4673aad7b1bad6772e3bd82d9964d5..3c59fb07e065e582dbb1311d2e6b7912a28f06dc 100644
--- a/chrome/browser/chromeos/login/easy_unlock/easy_unlock_tpm_key_manager.cc
+++ b/chrome/browser/chromeos/login/easy_unlock/easy_unlock_tpm_key_manager.cc
@@ -184,7 +184,7 @@ void EasyUnlockTpmKeyManager::RegisterLocalStatePrefs(
 
 // static
 void EasyUnlockTpmKeyManager::ResetLocalStateForUser(
-    const std::string& user_id) {
+    const user_manager::UserID& user_id) {
   if (!g_browser_process)
     return;
   PrefService* local_state = g_browser_process->local_state();
@@ -192,11 +192,11 @@ void EasyUnlockTpmKeyManager::ResetLocalStateForUser(
     return;
 
   DictionaryPrefUpdate update(local_state, prefs::kEasyUnlockLocalStateTpmKeys);
-  update->RemoveWithoutPathExpansion(user_id, NULL);
+  update->RemoveWithoutPathExpansion(user_id.GetUserEmail(), NULL);
 }
 
 EasyUnlockTpmKeyManager::EasyUnlockTpmKeyManager(
-    const std::string& user_id,
+    const user_manager::UserID& user_id,
     const std::string& username_hash,
     PrefService* local_state)
     : user_id_(user_id),
@@ -257,21 +257,21 @@ bool EasyUnlockTpmKeyManager::StartGetSystemSlotTimeoutMs(size_t timeout_ms) {
 }
 
 std::string EasyUnlockTpmKeyManager::GetPublicTpmKey(
-    const std::string& user_id) {
+    const user_manager::UserID& user_id) {
   if (!local_state_)
     return std::string();
   const base::DictionaryValue* dict =
       local_state_->GetDictionary(prefs::kEasyUnlockLocalStateTpmKeys);
   std::string key;
   if (dict)
-    dict->GetStringWithoutPathExpansion(user_id, &key);
+    dict->GetStringWithoutPathExpansion(user_id.GetUserEmail(), &key);
   std::string decoded;
   base::Base64Decode(key, &decoded);
   return decoded;
 }
 
 void EasyUnlockTpmKeyManager::SignUsingTpmKey(
-    const std::string& user_id,
+    const user_manager::UserID& user_id,
     const std::string& data,
     const base::Callback<void(const std::string& data)> callback) {
   std::string key = GetPublicTpmKey(user_id);
@@ -298,7 +298,7 @@ bool EasyUnlockTpmKeyManager::StartedCreatingTpmKeys() const {
          create_tpm_key_state_ == CREATE_TPM_KEY_DONE;
 }
 
-void EasyUnlockTpmKeyManager::SetKeyInLocalState(const std::string& user_id,
+void EasyUnlockTpmKeyManager::SetKeyInLocalState(const user_manager::UserID& user_id,
                                                  const std::string& value) {
   if (!local_state_)
     return;
@@ -307,7 +307,7 @@ void EasyUnlockTpmKeyManager::SetKeyInLocalState(const std::string& user_id,
   base::Base64Encode(value, &encoded);
   DictionaryPrefUpdate update(local_state_,
                               prefs::kEasyUnlockLocalStateTpmKeys);
-  update->SetStringWithoutPathExpansion(user_id, encoded);
+  update->SetStringWithoutPathExpansion(user_id.GetUserEmail(), encoded);
 }
 
 void EasyUnlockTpmKeyManager::OnUserTPMInitialized(