Pref service: add support for tracked prefs.

services/preferences/persistent_pref_store_impl.h

Index: services/preferences/persistent_pref_store_impl.h
diff --git a/services/preferences/persistent_pref_store_impl.h b/services/preferences/persistent_pref_store_impl.h
index 544cbe2f533d68b3f0593f59b3ab879ce3da7a1b..49d9cd93b62812a5996a6f9c6c6cc38b98d9d862 100644
--- a/services/preferences/persistent_pref_store_impl.h
+++ b/services/preferences/persistent_pref_store_impl.h
@@ -28,7 +28,6 @@ class PersistentPrefStoreImpl : public PrefStore::Observer {
   // called when it becomes true.
   PersistentPrefStoreImpl(
       scoped_refptr<PersistentPrefStore> backing_pref_store,
-      mojom::TrackedPreferenceValidationDelegatePtr validation_delegate,
       base::OnceClosure on_initialized);
 
   ~PersistentPrefStoreImpl() override;
@@ -56,7 +55,6 @@ class PersistentPrefStoreImpl : public PrefStore::Observer {
   void OnConnectionError(Connection* connection);
 
   scoped_refptr<PersistentPrefStore> backing_pref_store_;
-  mojom::TrackedPreferenceValidationDelegatePtr validation_delegate_;
 
   bool initializing_ = false;