Add a screen to migrate filesystem encryption from eCryptfs to ext4 crypto.

chrome/browser/chromeos/login/existing_user_controller.h

Index: chrome/browser/chromeos/login/existing_user_controller.h
diff --git a/chrome/browser/chromeos/login/existing_user_controller.h b/chrome/browser/chromeos/login/existing_user_controller.h
index 6a32f38dc573b91b98ebaf631bc5938a80317f5f..fc6f551564eb5353be2a258d2f1b8626931dfedb 100644
--- a/chrome/browser/chromeos/login/existing_user_controller.h
+++ b/chrome/browser/chromeos/login/existing_user_controller.h
@@ -163,6 +163,7 @@ class ExistingUserController
   void OnAuthSuccess(const UserContext& user_context) override;
   void OnOffTheRecordAuthSuccess() override;
   void OnPasswordChangeDetected() override;
+  void OnOldEncryptionDetected() override;
   void WhiteListCheckFailed(const std::string& email) override;
   void PolicyLoadFailed() override;
   void SetAuthFlowOffline(bool offline) override;
@@ -206,6 +207,9 @@ class ExistingUserController
   // Shows "kiosk auto-launch permission" screen.
   void ShowKioskAutolaunchScreen();
 
+  // Shows "filesystem encryption migration" screen.
+  void ShowEncryptionMigrationScreen();
+
   // Shows "critical TPM error" screen.
   void ShowTPMError();