Pref service: add persistent pref store frontend and backend.

services/preferences/user_prefs.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_USER_PREFS_H_
+#define SERVICES_PREFERENCES_USER_PREFS_H_
+
+#include <memory>
+#include <unordered_map>
+#include <vector>
+
+#include "base/macros.h"
+#include "services/preferences/public/interfaces/preferences.mojom.h"
+#include "services/preferences/public/interfaces/tracked_preference_validation_delegate.mojom.h"
+
+namespace base {
+class Value;
+}
+
+namespace prefs {
+
+class UserPrefs : public mojom::PersistentPrefStoreConnector,

[tibell, 2017/03/10 02:18:27]

Sorry to be a pain, but I think it would be nice to have a consistent naming
scheme for the "client" and "server" part of our pref stores. Right now we have
*Client and *Impl, respectively. Could this be called PersistentPrefStoreImpl
for consistency?

[Sam McNally, 2017/03/10 02:43:25]

Done.

+                  public PrefStore::Observer {
+ public:
+  UserPrefs(scoped_refptr<PersistentPrefStore> backing_pref_store,
+            mojom::TrackedPreferenceValidationDelegatePtr validation_delegate);
+
+  ~UserPrefs() override;
+
+  // mojom::PersistentPrefStoreConnector override:
+  void Connect(const ConnectCallback& callback) override;
+
+ private:
+  class Connection;
+
+  void SetValue(const std::string& key,
+                std::unique_ptr<base::Value> value,
+                uint32_t flags);
+
+  void CommitPendingWrite();
+  void SchedulePendingLossyWrites();
+  void ClearMutableValues();
+
+  // PrefStore::Observer:
+  void OnPrefValueChanged(const std::string& key) override;
+  void OnInitializationCompleted(bool succeeded) override;
+
+  void CallConnectCallback(
+      const mojom::PersistentPrefStoreConnector::ConnectCallback& callback);
+  void OnConnectionError(Connection* connection);
+
+  scoped_refptr<PersistentPrefStore> backing_pref_store_;
+  mojom::TrackedPreferenceValidationDelegatePtr validation_delegate_;
+
+  bool initializing_ = false;
+  std::vector<ConnectCallback> pending_connect_callbacks_;
+
+  std::unordered_map<Connection*, std::unique_ptr<Connection>> connections_;

[tibell, 2017/03/10 02:18:27]

Could this just be set<std::unique_ptr<Connection>>?

[Sam McNally, 2017/03/10 02:43:25]

Lookup by unique_ptr is inefficient.

+
+  DISALLOW_COPY_AND_ASSIGN(UserPrefs);
+};
+
+}  // namespace prefs
+
+#endif  // SERVICES_PREFERENCES_USER_PREFS_H_