Pref service: expose all read-only PrefStores through Mojo

services/preferences/public/cpp/pref_store_client.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_H_
+#define SERVICES_PREFERENCES_PUBLIC_CPP_PREF_STORE_CLIENT_H_
+
+#include <string>
+
+#include "base/macros.h"
+#include "base/observer_list.h"
+#include "base/values.h"
+#include "components/prefs/pref_store.h"
+#include "components/prefs/pref_value_map.h"
+#include "mojo/public/cpp/bindings/binding.h"
+#include "services/preferences/public/cpp/pref_store_manager_impl.h"
+#include "services/preferences/public/interfaces/preferences.mojom.h"
+
+namespace prefs {
+
+// TODO(tibell): Make PrefObserverStore use PrefStoreClient as a base class.
+
+// An implementation of PrefStore which uses prefs::mojom::PrefStore as
+// the backing store of the preferences.
+//
+// PrefStoreClient provides synchronous access to the preferences stored by the
+// backing store by caching them locally.
+class PrefStoreClient : public ::PrefStore, public mojom::PrefStoreObserver {
+ public:
+  explicit PrefStoreClient(mojom::PrefStoreConnectionPtr connection);
+
+  // PrefStore:
+  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;
+
+ private:
+  friend class PrefStoreClientTest;
+
+  ~PrefStoreClient() override;
+
+  // prefs::mojom::PreferenceObserver:
+  void OnPrefChanged(const std::string& key,
+                     std::unique_ptr<base::Value> value) override;
+  void OnInitializationCompleted(bool succeeded) override;
+
+  // Cached preferences.
+  std::unique_ptr<base::DictionaryValue> cached_prefs_;
+
+  base::ObserverList<PrefStore::Observer, true> observers_;
+
+  // Has the PrefStore we're observing been initialized?
+  bool initialized_;
+
+  mojo::Binding<mojom::PrefStoreObserver> observer_binding_;
+
+  DISALLOW_COPY_AND_ASSIGN(PrefStoreClient);
+};
+
+}  // namespace prefs
+
+#endif  // SERVICES_PREFERENCES_PUBLIC_CPP_PREF_STORE_CLIENT_H_