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

chrome/browser/signin/account_reconcilor_unittest.cc

Index: chrome/browser/signin/account_reconcilor_unittest.cc
diff --git a/chrome/browser/signin/account_reconcilor_unittest.cc b/chrome/browser/signin/account_reconcilor_unittest.cc
index fe138495977587bdc20e8e5090500867f90cc568..617008ca97775686c0849ad1d865bb7e1a178af8 100644
--- a/chrome/browser/signin/account_reconcilor_unittest.cc
+++ b/chrome/browser/signin/account_reconcilor_unittest.cc
@@ -32,6 +32,7 @@
 #include "components/signin/core/browser/test_signin_client.h"
 #include "components/signin/core/common/profile_management_switches.h"
 #include "components/signin/core/common/signin_switches.h"
+#include "components/user_manager/user_id.h"
 #include "content/public/test/test_browser_thread_bundle.h"
 #include "google_apis/gaia/gaia_constants.h"
 #include "google_apis/gaia/gaia_urls.h"
@@ -103,15 +104,13 @@ class AccountReconcilorTest : public ::testing::TestWithParam<bool> {
 
   MockAccountReconcilor* GetMockReconcilor();
 
-  std::string ConnectProfileToAccount(const std::string& gaia_id,
-                                      const std::string& username);
+  std::string ConnectProfileToAccount(const user_manager::UserID& user_id);
 
-  std::string PickAccountIdForAccount(const std::string& gaia_id,
-                                      const std::string& username);
+  std::string PickAccountIdForAccount(const user_manager::UserID& user_id);
 
   void SimulateAddAccountToCookieCompleted(
       GaiaCookieManagerService::Observer* observer,
-      const std::string& account_id,
+      const user_manager::UserID& user_id,
       const GoogleServiceAuthError& error);
 
   void SimulateCookieContentSettingsChanged(
@@ -220,21 +219,17 @@ MockAccountReconcilor* AccountReconcilorTest::GetMockReconcilor() {
 }
 
 std::string AccountReconcilorTest::ConnectProfileToAccount(
-    const std::string& gaia_id,
-    const std::string& username) {
-  const std::string account_id = PickAccountIdForAccount(gaia_id, username);
+    const user_manager::UserID& user_id) {
 #if !defined(OS_CHROMEOS)
   signin_manager()->set_password("password");
 #endif
-  signin_manager()->SetAuthenticatedAccountInfo(gaia_id, username);
-  token_service()->UpdateCredentials(account_id, "refresh_token");
+  signin_manager()->SetAuthenticatedAccountInfo(user_id);
+  token_service()->UpdateCredentials(user_id, "refresh_token");
   return account_id;
 }
 
-std::string AccountReconcilorTest::PickAccountIdForAccount(
-    const std::string& gaia_id,
-    const std::string& username) {
-  return account_tracker()->PickAccountIdForAccount(gaia_id, username);
+std::string AccountReconcilorTest::PickAccountIdForAccount(const user_manager::UserID& user_id) {
+  return account_tracker()->PickAccountIdForAccount(user_id);
 }
 
 void AccountReconcilorTest::SimulateAddAccountToCookieCompleted(