Pref service: add persistent pref store frontend and backend.

services/preferences/public/cpp/pref_store_client_mixin.h

Index: services/preferences/public/cpp/pref_store_client_mixin.h
diff --git a/services/preferences/public/cpp/pref_store_client_mixin.h b/services/preferences/public/cpp/pref_store_client_mixin.h
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+// 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>
+
+#include "base/macros.h"
+#include "base/observer_list.h"
+#include "mojo/public/cpp/bindings/binding.h"
+#include "services/preferences/public/interfaces/preferences.mojom.h"
+
+namespace base {
+class DictionaryValue;
+class Value;
+}
+
+namespace prefs {
+
+// An mixin implementation of PrefStore which uses prefs::mojom::PrefStore as
+// the backing store of the preferences.
+//
+// PrefStoreClientMixin provides synchronous access to the preferences stored by
+// the backing store by caching them locally.
+template <typename BasePrefStore>
+class PrefStoreClientMixin : public BasePrefStore,
+                             public mojom::PrefStoreObserver {
+ public:
+  PrefStoreClientMixin();
+
+  // BasePrefStore:
+  void AddObserver(PrefStore::Observer* observer) override;
+  void RemoveObserver(PrefStore::Observer* observer) override;
+  bool HasObservers() const override;
+  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,
+            bool initialized,
+            mojom::PrefStoreObserverRequest observer_request);
+
+  base::DictionaryValue& GetMutableValues();
+  void ReportPrefValueChanged(const std::string& key);
+
+ private:
+  // prefs::mojom::PreferenceObserver:
+  void OnPrefChanged(const std::string& key,
+                     std::unique_ptr<base::Value> value) override;
+  void OnInitializationCompleted(bool succeeded) override;
+
+  // 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_