[Sync] Add ability to save/restore Nigori to SyncEncryptionHandlerImpl

sync/internal_api/js_sync_encryption_handler_observer.h

Index: sync/internal_api/js_sync_encryption_handler_observer.h
diff --git a/sync/internal_api/js_sync_encryption_handler_observer.h b/sync/internal_api/js_sync_encryption_handler_observer.h
index 82d5743f04e4c5ebfc03326bf8ba5d9a77b761d2..206e59bbde95b28fa723f6c7f23f84819d85f736 100644
--- a/sync/internal_api/js_sync_encryption_handler_observer.h
+++ b/sync/internal_api/js_sync_encryption_handler_observer.h
@@ -45,6 +45,8 @@ class SYNC_EXPORT_PRIVATE JsSyncEncryptionHandlerObserver
   void OnCryptographerStateChanged(Cryptographer* cryptographer) override;
   void OnPassphraseTypeChanged(PassphraseType type,
                                base::Time explicit_passphrase_time) override;
+  void OnLocalSetCustomPassphrase(
+      const SyncEncryptionHandler::NigoriState& nigori_state) override;
 
  private:
   void HandleJsEvent(const tracked_objects::Location& from_here,