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

components/proximity_auth/screenlock_bridge.cc

Index: components/proximity_auth/screenlock_bridge.cc
diff --git a/components/proximity_auth/screenlock_bridge.cc b/components/proximity_auth/screenlock_bridge.cc
index 2af83781dc0dfe986a4ffb3114cf1781361ab2ce..f0fc044f23846017800e1096726e7856fa3f135a 100644
--- a/components/proximity_auth/screenlock_bridge.cc
+++ b/components/proximity_auth/screenlock_bridge.cc
@@ -7,6 +7,7 @@
 #include "base/logging.h"
 #include "base/strings/string16.h"
 #include "components/proximity_auth/proximity_auth_client.h"
+#include "components/user_manager/user_id.h"
 
 #if defined(OS_CHROMEOS)
 #include "chromeos/dbus/dbus_thread_manager.h"
@@ -50,7 +51,7 @@ std::string GetIdForIcon(ScreenlockBridge::UserPodCustomIcon icon) {
 }  // namespace
 
 ScreenlockBridge::ScreenlockBridge(ProximityAuthClient* client)
-    : client_(client), lock_handler_(nullptr) {
+    : client_(client), lock_handler_(nullptr), focused_user_id_(std::string(), std::string()) {
   DCHECK(client_);
 }
 
@@ -139,7 +140,7 @@ void ScreenlockBridge::SetLockHandler(LockHandler* lock_handler) {
     FOR_EACH_OBSERVER(Observer, observers_, OnScreenDidUnlock(screen_type));
 }
 
-void ScreenlockBridge::SetFocusedUser(const std::string& user_id) {
+void ScreenlockBridge::SetFocusedUser(const user_manager::UserID& user_id) {
   if (user_id == focused_user_id_)
     return;
   focused_user_id_ = user_id;
@@ -161,8 +162,10 @@ void ScreenlockBridge::Lock(content::BrowserContext* browser_context) {
 }
 
 void ScreenlockBridge::Unlock(content::BrowserContext* browser_context) {
-  if (lock_handler_)
-    lock_handler_->Unlock(client_->GetAuthenticatedUsername(browser_context));
+  if (lock_handler_) {
+    const user_manager::UserID user_id(user_manager::UserID::FromUserEmail(client_->GetAuthenticatedUsername(browser_context)));
+    lock_handler_->Unlock(user_id);
+  }
 }
 
 void ScreenlockBridge::AddObserver(Observer* observer) {