cros: Use ScreenManager as a component instead of deriving WizardController from it

chrome/browser/chromeos/login/screen_manager.h

Index: chrome/browser/chromeos/login/screen_manager.h
diff --git a/chrome/browser/chromeos/login/screen_manager.h b/chrome/browser/chromeos/login/screen_manager.h
index 360d2b28e96c573a667e271613c148879567e9ff..e0b1383e26da8f95c1defdb389b2814558d8b287 100644
--- a/chrome/browser/chromeos/login/screen_manager.h
+++ b/chrome/browser/chromeos/login/screen_manager.h
@@ -6,26 +6,26 @@
 #define CHROME_BROWSER_CHROMEOS_LOGIN_SCREEN_MANAGER_H_
 
 #include <map>
+#include <memory>
 #include <string>
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
-#include "base/memory/linked_ptr.h"
 #include "chrome/browser/chromeos/login/screens/base_screen.h"
 
 namespace chromeos {
 
+class WizardController;
+
 // Class that manages creation and ownership of screens.
 class ScreenManager {
  public:
-  ScreenManager();
-  virtual ~ScreenManager();
+  // |wizard_controller| is not owned by this class.
+  explicit ScreenManager(WizardController* wizard_controller);
+  ~ScreenManager();
 
   // Getter for screen with lazy initialization.
-  virtual BaseScreen* GetScreen(OobeScreen screen);
-
-  // Factory for screen instances.
-  virtual BaseScreen* CreateScreen(OobeScreen screen) = 0;
+  BaseScreen* GetScreen(OobeScreen screen);
 
   bool HasScreen(OobeScreen screen);
 
@@ -37,8 +37,11 @@ class ScreenManager {
   friend class WizardInProcessBrowserTest;
   friend class WizardControllerBrokenLocalStateTest;
 
-  // Screens.
-  std::map<OobeScreen, linked_ptr<BaseScreen>> screens_;
+  // Created screens.
+  std::map<OobeScreen, std::unique_ptr<BaseScreen>> screens_;
+
+  // Used to allocate BaseScreen instances. Unowned.
+  WizardController* wizard_controller_;
 
   DISALLOW_COPY_AND_ASSIGN(ScreenManager);
 };