Force encryption migration if the device supports ARC.

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

Index: chrome/browser/chromeos/login/screens/encryption_migration_screen.h
diff --git a/chrome/browser/chromeos/login/screens/encryption_migration_screen.h b/chrome/browser/chromeos/login/screens/encryption_migration_screen.h
index 5764afe5c51fc53ff5bcc9b2ef3cbaf401c0fcd6..d43bc019dbeb0b5cde1e376e6e7272e6ed5c132b 100644
--- a/chrome/browser/chromeos/login/screens/encryption_migration_screen.h
+++ b/chrome/browser/chromeos/login/screens/encryption_migration_screen.h
@@ -7,6 +7,7 @@
 
 #include "chrome/browser/chromeos/login/screens/base_screen.h"
 #include "chrome/browser/chromeos/login/screens/encryption_migration_screen_view.h"
+#include "chromeos/login/auth/login_performer.h"
 
 namespace chromeos {
 
@@ -16,6 +17,10 @@ class EncryptionMigrationScreen
     : public BaseScreen,
       public EncryptionMigrationScreenView::Delegate {
  public:
+  using ContinueLoginCallback =
+      base::OnceCallback<void(const UserContext&,
+                              LoginPerformer::AuthorizationMode)>;
+
   EncryptionMigrationScreen(BaseScreenDelegate* base_screen_delegate,
                             EncryptionMigrationScreenView* view);
   ~EncryptionMigrationScreen() override;
@@ -31,6 +36,10 @@ class EncryptionMigrationScreen
   // Sets the UserContext for a user whose cryptohome should be migrated.
   void SetUserContext(const UserContext& user_context);
 
+  // Sets a callback, which should be called when the user want to log in to the
+  // session from the migration UI.
+  void SetContinueLoginCallback(ContinueLoginCallback callback);
+
  private:
   EncryptionMigrationScreenView* view_;