user_manager component: Add UserManagerBase class.

chrome/browser/chromeos/login/users/user_manager.h

Index: chrome/browser/chromeos/login/users/user_manager.h
diff --git a/chrome/browser/chromeos/login/users/user_manager.h b/chrome/browser/chromeos/login/users/user_manager.h
index fe42e311ab0bb37bb433bbcf7a48e0193b23291d..b7c7ed3be5ba4cce09d31773b77494ceb60e9773 100644
--- a/chrome/browser/chromeos/login/users/user_manager.h
+++ b/chrome/browser/chromeos/login/users/user_manager.h
@@ -19,7 +19,7 @@ class RemoveUserDelegate;
 class UserImageManager;
 class SupervisedUserManager;
 
-// Base class for UserManagerImpl - provides a mechanism for discovering users
+// Interface for UserManagerBase - provides a mechanism for discovering users
 // who have logged into this Chrome OS device before and updating that list.
 class UserManager {
  public:
@@ -134,7 +134,7 @@ class UserManager {
 
   // Returns the email of the owner user. Returns an empty string if there is
   // no owner for the device.
-  virtual const std::string& GetOwnerEmail() = 0;
+  virtual const std::string& GetOwnerEmail() const = 0;
 
   // Indicates that a user with the given |user_id| has just logged in. The
   // persistent list is updated accordingly if the user is not ephemeral.