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

chrome/browser/chromeos/login/easy_unlock/bootstrap_manager.h

Index: chrome/browser/chromeos/login/easy_unlock/bootstrap_manager.h
diff --git a/chrome/browser/chromeos/login/easy_unlock/bootstrap_manager.h b/chrome/browser/chromeos/login/easy_unlock/bootstrap_manager.h
index 46955baf54ad8dde0ca0cb4922030df398712a21..97cf6d82af6552b890b87460b53b94b91e8a1bee 100644
--- a/chrome/browser/chromeos/login/easy_unlock/bootstrap_manager.h
+++ b/chrome/browser/chromeos/login/easy_unlock/bootstrap_manager.h
@@ -11,6 +11,10 @@
 
 class PrefRegistrySimple;
 
+namespace user_manager {
+class UserID;
+}
+
 namespace chromeos {
 
 // BootstrapManager manages bootstrap user specific values such as tracking
@@ -21,7 +25,7 @@ class BootstrapManager {
 
   class Delegate {
    public:
-    virtual void RemovePendingBootstrapUser(const std::string& user_id) = 0;
+    virtual void RemovePendingBootstrapUser(const user_manager::UserID& user_id) = 0;
 
    protected:
     virtual ~Delegate() {}
@@ -30,11 +34,11 @@ class BootstrapManager {
   explicit BootstrapManager(Delegate* delegate);
   ~BootstrapManager();
 
-  void AddPendingBootstrap(const std::string& user_id);
-  void FinishPendingBootstrap(const std::string& user_id);
+  void AddPendingBootstrap(const user_manager::UserID& user_id);
+  void FinishPendingBootstrap(const user_manager::UserID& user_id);
   void RemoveAllPendingBootstrap();
 
-  bool HasPendingBootstrap(const std::string& user_id) const;
+  bool HasPendingBootstrap(const user_manager::UserID& user_id) const;
 
  private:
   Delegate* delegate_;