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

chrome/browser/ui/ash/launcher/browser_status_monitor.h

Index: chrome/browser/ui/ash/launcher/browser_status_monitor.h
diff --git a/chrome/browser/ui/ash/launcher/browser_status_monitor.h b/chrome/browser/ui/ash/launcher/browser_status_monitor.h
index b0a4e5bda5f9d75982cf1590ea1c19cec073cd27..4ede3114d4c97ea1d75ff2fdb2bf46a7a8bbea70 100644
--- a/chrome/browser/ui/ash/launcher/browser_status_monitor.h
+++ b/chrome/browser/ui/ash/launcher/browser_status_monitor.h
@@ -27,6 +27,10 @@ class ActivationClient;
 }
 }  // namespace aura
 
+namespace user_manager {
+class UserID;
+}
+
 class Browser;
 
 // BrowserStatusMonitor monitors creation/deletion of Browser and its
@@ -45,7 +49,7 @@ class BrowserStatusMonitor : public aura::client::ActivationChangeObserver,
   // Note that this function is called by the ChromeLauncherController to be
   // able to do the activation in a proper order - rather then setting an
   // observer.
-  virtual void ActiveUserChanged(const std::string& user_email) {}
+  virtual void ActiveUserChanged(const user_manager::UserID& user_email) {}
 
   // A shortcut to call the ChromeLauncherController's UpdateAppState().
   void UpdateAppItemState(content::WebContents* contents,