Switch base::Value typemapping to be by value instead of by unique_ptr.

services/preferences/public/cpp/pref_store_client_mixin.h

 // Copyright 2017 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 SERVICES_PREFERENCES_PUBLIC_CPP_PREF_STORE_CLIENT_MIXIN_H_
 #define SERVICES_PREFERENCES_PUBLIC_CPP_PREF_STORE_CLIENT_MIXIN_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 27 matching lines @@
   bool IsInitializationComplete() const override;
   bool GetValue(const std::string& key,
                 const base::Value** result) const override;
   std::unique_ptr<base::DictionaryValue> GetValues() const override;
 
  protected:
   ~PrefStoreClientMixin() override;
 
   // Initializes |this|. This must be called before any of the other public or
   // protected member functions.
-  void Init(std::unique_ptr<base::DictionaryValue> initial_prefs,
+  void Init(const base::DictionaryValue* initial_prefs,
             bool initialized,
             mojom::PrefStoreObserverRequest observer_request);
 
   base::DictionaryValue& GetMutableValues();
   void ReportPrefValueChanged(const std::string& key);
 
  private:
   // prefs::mojom::PreferenceObserver:
   void OnPrefsChanged(std::vector<mojom::PrefUpdatePtr> updates) override;
   void OnInitializationCompleted(bool succeeded) override;
 
-  void OnPrefChanged(const std::string& key,
-                     std::unique_ptr<base::Value> value);
+  void OnPrefChanged(const std::string& key, base::Optional<base::Value> value);
 
   // Cached preferences.
   // If null, indicates that initialization failed.
   std::unique_ptr<base::DictionaryValue> cached_prefs_;
 
   base::ObserverList<PrefStore::Observer, true> observers_;
 
   // Has the PrefStore we're observing been initialized?
   bool initialized_ = false;
 
   mojo::Binding<mojom::PrefStoreObserver> observer_binding_;
 
   DISALLOW_COPY_AND_ASSIGN(PrefStoreClientMixin);
 };
 
 extern template class PrefStoreClientMixin<::PrefStore>;
 extern template class PrefStoreClientMixin<::PersistentPrefStore>;
 
 }  // namespace prefs
 
 #endif  // SERVICES_PREFERENCES_PUBLIC_CPP_PREF_STORE_CLIENT_MIXIN_H_