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

components/user_manager/user_info_impl.cc

Index: components/user_manager/user_info_impl.cc
diff --git a/components/user_manager/user_info_impl.cc b/components/user_manager/user_info_impl.cc
index 6aa21a8adb71cf0d13822212cd78f55b3fb7542b..7844c6652d90969b5f46534e3a7ffcf2cced0d9d 100644
--- a/components/user_manager/user_info_impl.cc
+++ b/components/user_manager/user_info_impl.cc
@@ -9,7 +9,7 @@
 
 namespace user_manager {
 
-UserInfoImpl::UserInfoImpl() {
+UserInfoImpl::UserInfoImpl() : user_id_(UserID::FromUserEmail(GetEmail())) {
 }
 
 UserInfoImpl::~UserInfoImpl() {
@@ -27,8 +27,8 @@ std::string UserInfoImpl::GetEmail() const {
   return "stub-user@domain.com";
 }
 
-std::string UserInfoImpl::GetUserID() const {
-  return GetEmail();
+const UserID& UserInfoImpl::GetUserID() const {
+  return user_id_;
 }
 
 const gfx::ImageSkia& UserInfoImpl::GetImage() const {