cros: Remove usage of GaiaScreenHandler outside of login/webui.

chrome/browser/chromeos/login/screens/gaia_screen.h

Index: chrome/browser/chromeos/login/screens/gaia_screen.h
diff --git a/chrome/browser/chromeos/login/screens/gaia_screen.h b/chrome/browser/chromeos/login/screens/gaia_screen.h
index f19671190a3f54374fab79f893b3cc68d64a1453..680af80b5aaa391028643d619a11e47969ad1730 100644
--- a/chrome/browser/chromeos/login/screens/gaia_screen.h
+++ b/chrome/browser/chromeos/login/screens/gaia_screen.h
@@ -13,22 +13,21 @@
 
 namespace chromeos {
 
-class LoginDisplayWebUIHandler;
-class GaiaScreenHandler;
+class GaiaView;
 
 // This class represents GAIA screen: login screen that is responsible for
 // GAIA-based sign-in.
 class GaiaScreen {
  public:
-  GaiaScreen();
-  virtual ~GaiaScreen();
-  void SetLegacyHandler(LoginDisplayWebUIHandler* handler);
-  void SetScreenHandler(GaiaScreenHandler* handler);
+  GaiaScreen() = default;
+  virtual ~GaiaScreen() = default;
+
+  void set_view(GaiaView* view) { view_ = view; }
+
   void MaybePreloadAuthExtension();
 
  private:
-  LoginDisplayWebUIHandler* legacy_handler_;
-  GaiaScreenHandler* screen_handler_;
+  GaiaView* view_ = nullptr;
 
   DISALLOW_COPY_AND_ASSIGN(GaiaScreen);
 };