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

chrome/browser/chromeos/login/wizard_controller.h

Index: chrome/browser/chromeos/login/wizard_controller.h
diff --git a/chrome/browser/chromeos/login/wizard_controller.h b/chrome/browser/chromeos/login/wizard_controller.h
index d11dffc256f3caa193e624007a446505ee6de3c4..8e9d150043a41ebab3df603f4c958396d70e6307 100644
--- a/chrome/browser/chromeos/login/wizard_controller.h
+++ b/chrome/browser/chromeos/login/wizard_controller.h
@@ -51,7 +51,6 @@ struct TimeZoneResponseData;
 // Class that manages control flow between wizard screens. Wizard controller
 // interacts with screen controllers to move the user between screens.
 class WizardController : public BaseScreenDelegate,
-                         public ScreenManager,
                          public EulaScreen::Delegate,
                          public ControllerPairingScreen::Delegate,
                          public HostPairingScreen::Delegate,
@@ -113,13 +112,19 @@ class WizardController : public BaseScreenDelegate,
   // Returns true if the current wizard instance has reached the login screen.
   bool login_screen_started() const { return login_screen_started_; }
 
-  // ScreenManager implementation.
-  BaseScreen* GetScreen(OobeScreen screen) override;
-  BaseScreen* CreateScreen(OobeScreen screen) override;
+  // Returns a given screen. Creates it lazily.
+  BaseScreen* GetScreen(OobeScreen screen);
+
+  // Returns the current ScreenManager instance.
+  ScreenManager* screen_manager() { return &screen_manager_; }
 
   // Volume percent at which spoken feedback is still audible.
   static const int kMinAudibleOutputVolumePercent;
 
+  // Allocate a given BaseScreen for the given |Screen|. Used by
+  // |screen_manager_|.
+  BaseScreen* CreateScreen(OobeScreen screen);
+
  private:
   // Show specific screen.
   void ShowNetworkScreen();
@@ -300,6 +305,8 @@ class WizardController : public BaseScreenDelegate,
   // attestation-based enrollment if appropriate.
   void StartEnrollmentScreen(bool force_interactive);
 
+  ScreenManager screen_manager_;
+
   // Whether to skip any screens that may normally be shown after login
   // (registration, Terms of Service, user image selection).
   static bool skip_post_login_screens_;