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

chrome/browser/chromeos/login/users/multi_profile_user_controller.cc

Index: chrome/browser/chromeos/login/users/multi_profile_user_controller.cc
diff --git a/chrome/browser/chromeos/login/users/multi_profile_user_controller.cc b/chrome/browser/chromeos/login/users/multi_profile_user_controller.cc
index e1733004c33b8498b9b61207681b6c05dfd0f717..8b01f34d21dbfa3643d4d7cf11ddcacc962e9a41 100644
--- a/chrome/browser/chromeos/login/users/multi_profile_user_controller.cc
+++ b/chrome/browser/chromeos/login/users/multi_profile_user_controller.cc
@@ -18,6 +18,7 @@
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/common/pref_names.h"
 #include "components/user_manager/user.h"
+#include "components/user_manager/user_id.h"
 #include "components/user_manager/user_manager.h"
 #include "google_apis/gaia/gaia_auth_util.h"
 
@@ -96,7 +97,7 @@ MultiProfileUserController::GetPrimaryUserPolicy() {
     return ALLOWED;
 
   // Don't allow any secondary profiles if the primary profile is tainted.
-  if (policy::PolicyCertServiceFactory::UsedPolicyCertificates(user->email())) {
+  if (policy::PolicyCertServiceFactory::UsedPolicyCertificates(user->GetUserID())) {
     // Check directly in local_state before checking if the primary user has
     // a PolicyCertService. His profile may have been tainted previously though
     // he didn't get a PolicyCertService created for this session.
@@ -125,24 +126,24 @@ MultiProfileUserController::GetPrimaryUserPolicy() {
 }
 
 bool MultiProfileUserController::IsUserAllowedInSession(
-    const std::string& user_email,
+    const user_manager::UserID& user_id,
     MultiProfileUserController::UserAllowedInSessionReason* reason) const {
   user_manager::UserManager* user_manager = user_manager::UserManager::Get();
   CHECK(user_manager);
 
   const user_manager::User* primary_user = user_manager->GetPrimaryUser();
-  std::string primary_user_email;
+  user_manager::UserID primary_user_id = user_manager::UserID(std::string(), std::string());

[Denis Kuznetsov (DE-MUC), 2015/06/10 16:50:45]

EmptyGaiaID() ?

   if (primary_user)
-    primary_user_email = primary_user->email();
+    primary_user_id = primary_user->GetUserID();
 
   // Always allow if there is no primary user or user being checked is the
   // primary user.
-  if (primary_user_email.empty() || primary_user_email == user_email)
+  if (primary_user_id.empty() || primary_user_id == user_id)
     return SetUserAllowedReason(reason, ALLOWED);
 
   // Don't allow profiles potentially tainted by data fetched with policy-pushed
   // certificates to join a multiprofile session.
-  if (policy::PolicyCertServiceFactory::UsedPolicyCertificates(user_email))
+  if (policy::PolicyCertServiceFactory::UsedPolicyCertificates(user_id))
     return SetUserAllowedReason(reason, NOT_ALLOWED_POLICY_CERT_TAINTED);
 
   UserAllowedInSessionReason primary_user_policy = GetPrimaryUserPolicy();
@@ -150,7 +151,7 @@ bool MultiProfileUserController::IsUserAllowedInSession(
     return SetUserAllowedReason(reason, primary_user_policy);
 
   // The user must have 'unrestricted' policy to be a secondary user.
-  const std::string behavior = GetCachedValue(user_email);
+  const std::string behavior = GetCachedValue(user_id);
   return SetUserAllowedReason(
       reason,
       behavior == kBehaviorUnrestricted ? ALLOWED : NOT_ALLOWED_POLICY_FORBIDS);
@@ -174,30 +175,30 @@ void MultiProfileUserController::StartObserving(Profile* user_profile) {
 }
 
 void MultiProfileUserController::RemoveCachedValues(
-    const std::string& user_email) {
+    const user_manager::UserID& user_id) {
   DictionaryPrefUpdate update(local_state_,
                               prefs::kCachedMultiProfileUserBehavior);
-  update->RemoveWithoutPathExpansion(user_email, NULL);
-  policy::PolicyCertServiceFactory::ClearUsedPolicyCertificates(user_email);
+  update->RemoveWithoutPathExpansion(user_id.GetUserEmail(), NULL);
+  policy::PolicyCertServiceFactory::ClearUsedPolicyCertificates(user_id);
 }
 
 std::string MultiProfileUserController::GetCachedValue(
-    const std::string& user_email) const {
+    const user_manager::UserID& user_id) const {
   const base::DictionaryValue* dict =
       local_state_->GetDictionary(prefs::kCachedMultiProfileUserBehavior);
   std::string value;
-  if (dict && dict->GetStringWithoutPathExpansion(user_email, &value))
+  if (dict && dict->GetStringWithoutPathExpansion(user_id.GetUserEmail(), &value))
     return SanitizeBehaviorValue(value);
 
   return std::string(kBehaviorUnrestricted);
 }
 
 void MultiProfileUserController::SetCachedValue(
-    const std::string& user_email,
+    const user_manager::UserID& user_id,
     const std::string& behavior) {
   DictionaryPrefUpdate update(local_state_,
                               prefs::kCachedMultiProfileUserBehavior);
-  update->SetStringWithoutPathExpansion(user_email,
+  update->SetStringWithoutPathExpansion(user_id.GetUserEmail(),
                                         SanitizeBehaviorValue(behavior));
 }
 
@@ -207,8 +208,8 @@ void MultiProfileUserController::CheckSessionUsers() {
   for (user_manager::UserList::const_iterator it = users.begin();
        it != users.end();
        ++it) {
-    if (!IsUserAllowedInSession((*it)->email(), NULL)) {
-      delegate_->OnUserNotAllowed((*it)->email());
+    if (!IsUserAllowedInSession((*it)->GetUserID(), NULL)) {
+      delegate_->OnUserNotAllowed((*it)->GetUserID());
       return;
     }
   }
@@ -219,6 +220,7 @@ void MultiProfileUserController::OnUserPrefChanged(
   std::string user_email = user_profile->GetProfileUserName();
   CHECK(!user_email.empty());
   user_email = gaia::CanonicalizeEmail(user_email);
+  const user_manager::UserID user_id(std::string() /* gaia_id */, user_email);

[Denis Kuznetsov (DE-MUC), 2015/06/10 16:50:45]

FromUserEmail()

 
   PrefService* prefs = user_profile->GetPrefs();
   if (prefs->FindPreference(prefs::kMultiProfileUserBehavior)
@@ -227,11 +229,11 @@ void MultiProfileUserController::OnUserPrefChanged(
     // TODO(xiyuan): Remove this after M35.
     DictionaryPrefUpdate update(local_state_,
                                 prefs::kCachedMultiProfileUserBehavior);
-    update->RemoveWithoutPathExpansion(user_email, NULL);
+    update->RemoveWithoutPathExpansion(user_id.GetUserEmail(), NULL);
   } else {
     const std::string behavior =
         prefs->GetString(prefs::kMultiProfileUserBehavior);
-    SetCachedValue(user_email, behavior);
+    SetCachedValue(user_id, behavior);
   }
 
   CheckSessionUsers();