Delete the PreferenceMACs on profile deletion.

services/preferences/tracked/pref_hash_filter.cc

Index: services/preferences/tracked/pref_hash_filter.cc
diff --git a/services/preferences/tracked/pref_hash_filter.cc b/services/preferences/tracked/pref_hash_filter.cc
index 29d6b9ab830891d3388ed91e6c14957deed32465..578901297d080d3df173052388acd8a2c33352e9 100644
--- a/services/preferences/tracked/pref_hash_filter.cc
+++ b/services/preferences/tracked/pref_hash_filter.cc
@@ -201,6 +201,16 @@ PrefFilter::OnWriteCallbackPair PrefHashFilter::FilterSerializeData(
   return callback_pair;
 }
 
+void PrefHashFilter::CleanupForProfileDeletion() {
+  if (external_validation_hash_store_pair_) {
+    external_validation_hash_store_pair_->second.get()->Reset();
+
+    // The PrefStore will attempt to flush the preferences of a deleted profile.
+    // Clear the external store pair to avoid re-writing to it.
+    external_validation_hash_store_pair_.reset();
+  }
+}
+
 void PrefHashFilter::FinalizeFilterOnLoad(
     const PostFilterOnLoadCallback& post_filter_on_load_callback,
     std::unique_ptr<base::DictionaryValue> pref_store_contents,