Delete the PreferenceMACs on profile deletion.

components/prefs/persistent_pref_store.h

Index: components/prefs/persistent_pref_store.h
diff --git a/components/prefs/persistent_pref_store.h b/components/prefs/persistent_pref_store.h
index b3ff5f466c4c4259a25596b05f76c9775fec6331..3be5816a53b5929ed06aebd5e8da746105e4ee61 100644
--- a/components/prefs/persistent_pref_store.h
+++ b/components/prefs/persistent_pref_store.h
@@ -79,6 +79,9 @@ class COMPONENTS_PREFS_EXPORT PersistentPrefStore : public WriteablePrefStore {
   // It should be called only for Incognito pref store.
   virtual void ClearMutableValues() = 0;
 
+  // Cleans preference data that may have been saved outside of the store.
+  virtual void OnStoreDeletionFromDisk() = 0;
+
  protected:
   ~PersistentPrefStore() override {}
 };