Delete the PreferenceMACs on profile deletion.

services/preferences/public/interfaces/preferences.mojom

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 module prefs.mojom;
 
 import "mojo/common/file_path.mojom";
 import "mojo/common/string16.mojom";
 import "mojo/common/values.mojom";
 import "services/preferences/public/interfaces/tracked_preference_validation_delegate.mojom";
@@ skipping 119 matching lines @@
   // Requests that the pref service transmits its value for a pref (or sub-pref
   // if |sub_pref_path| is non-empty). The value will be transmitted over the
   // corresponding PrefStoreObserver interface previous returned by
   // PrefStoreConnector.Connect().
   RequestValue(string key, array<string> sub_pref_path);
 
   // These mirror the C++ PersistentPrefStore methods.
   CommitPendingWrite() => ();
   SchedulePendingLossyWrites();
   ClearMutableValues();
+  OnStoreDeletionFromDisk();
 };
 
 // A registry of all prefs registered by a single client.
 struct PrefRegistry {
   // A list of pref keys that are private to this client. This client claims
   // exclusive access to these prefs.
   array<string> private_registrations;
 
   // A list of pref keys that are public, but owned by another client.
   array<string> foreign_registrations;
@@ skipping 54 matching lines @@
   uint64 reporting_id;
   string name;
   EnforcementLevel enforcement_level;
   PrefTrackingStrategy strategy;
   ValueType value_type;
 };
 
 interface ResetOnLoadObserver {
   OnResetOnLoad();
 };