Delete the PreferenceMACs on profile deletion.

services/preferences/tracked/pref_hash_filter.h

Index: services/preferences/tracked/pref_hash_filter.h
diff --git a/services/preferences/tracked/pref_hash_filter.h b/services/preferences/tracked/pref_hash_filter.h
index 6467eb10dba6e7091984f0f92fda23c965f4f2a0..bdc9b621c9b7034d58ca4b1aa14a0104859096e4 100644
--- a/services/preferences/tracked/pref_hash_filter.h
+++ b/services/preferences/tracked/pref_hash_filter.h
@@ -92,6 +92,8 @@ class PrefHashFilter : public InterceptablePrefFilter {
   OnWriteCallbackPair FilterSerializeData(
       base::DictionaryValue* pref_store_contents) override;
 
+  void OnStoreDeletionFromDisk() override;
+
  private:
   // InterceptablePrefFilter implementation.
   void FinalizeFilterOnLoad(
@@ -137,7 +139,7 @@ class PrefHashFilter : public InterceptablePrefFilter {
   // A store and contents on which to perform extra validations without
   // triggering resets.
   // Will be null if the platform does not support external validation.
-  const base::Optional<StoreContentsPair> external_validation_hash_store_pair_;
+  base::Optional<StoreContentsPair> external_validation_hash_store_pair_;
 
   // Notified if a reset occurs in a call to FilterOnLoad.
   prefs::mojom::ResetOnLoadObserverPtr reset_on_load_observer_;