Delete the PreferenceMACs on profile deletion.

components/prefs/in_memory_pref_store.h

 // Copyright (c) 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.
 
 #ifndef COMPONENTS_PREFS_IN_MEMORY_PREF_STORE_H_
 #define COMPONENTS_PREFS_IN_MEMORY_PREF_STORE_H_
 
 #include <stdint.h>
 
 #include <string>
@@ skipping 30 matching lines @@
   void SetValueSilently(const std::string& key,
                         std::unique_ptr<base::Value> value,
                         uint32_t flags) override;
   void RemoveValue(const std::string& key, uint32_t flags) override;
   bool ReadOnly() const override;
   PrefReadError GetReadError() const override;
   PersistentPrefStore::PrefReadError ReadPrefs() override;
   void ReadPrefsAsync(ReadErrorDelegate* error_delegate) override {}
   void SchedulePendingLossyWrites() override {}
   void ClearMutableValues() override {}
+  void OnStoreDeletionFromDisk() override {}
 
  protected:
   ~InMemoryPrefStore() override;
 
  private:
   // Stores the preference values.
   PrefValueMap prefs_;
 
   base::ObserverList<PrefStore::Observer, true> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(InMemoryPrefStore);
 };
 
 #endif  // COMPONENTS_PREFS_IN_MEMORY_PREF_STORE_H_