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

sync/sessions/model_type_registry.h

Index: sync/sessions/model_type_registry.h
diff --git a/sync/sessions/model_type_registry.h b/sync/sessions/model_type_registry.h
index ccfc117b29a16cf3d4138cbb2bcc11382dae8adc..1176067d64ad664c863b98b97e9b3eba85b088ae 100644
--- a/sync/sessions/model_type_registry.h
+++ b/sync/sessions/model_type_registry.h
@@ -83,6 +83,8 @@ class SYNC_EXPORT_PRIVATE ModelTypeRegistry
   void OnCryptographerStateChanged(Cryptographer* cryptographer) override;
   void OnPassphraseTypeChanged(PassphraseType type,
                                base::Time passphrase_time) override;
+  void OnLocalSetCustomPassphrase(
+      const SyncEncryptionHandler::NigoriState& nigori_state) override;
 
   // Gets the set of enabled types.
   ModelTypeSet GetEnabledTypes() const;