chrome.settingsPrivate: Implement onPrefsChanged event handling.

chrome/browser/extensions/api/settings_private/settings_private_event_router.h

+// Copyright 2015 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 CHROME_BROWSER_EXTENSIONS_API_SETTINGS_PRIVATE_SETTINGS_PRIVATE_EVENT_ROUTER_H_
+#define CHROME_BROWSER_EXTENSIONS_API_SETTINGS_PRIVATE_SETTINGS_PRIVATE_EVENT_ROUTER_H_
+
+#include "base/prefs/pref_change_registrar.h"
+#include "components/keyed_service/core/keyed_service.h"
+#include "extensions/browser/event_router.h"
+
+namespace content {
+class BrowserContext;
+}
+
+namespace extensions {
+
+class SettingsPrivateDelegate;
+
+// This is an event router that will observe listeners to pref changes on the
+// appropriate pref service(s) and notify listeners on the JavaScript
+// settingsPrivate API.
+class SettingsPrivateEventRouter : public KeyedService,
+                                   public EventRouter::Observer {
+ public:
+  static SettingsPrivateEventRouter* Create(
+      content::BrowserContext* browser_context);
+  ~SettingsPrivateEventRouter() override;
+
+ protected:
+  SettingsPrivateEventRouter() {}
+  explicit SettingsPrivateEventRouter(content::BrowserContext* context);
+
+  // KeyedService overrides:
+  void Shutdown() override;
+
+  // EventRouter::Observer overrides:
+  void OnListenerAdded(const EventListenerInfo& details) override;
+  void OnListenerRemoved(const EventListenerInfo& details) override;
+
+  // This registrar monitors for user prefs changes.
+  PrefChangeRegistrar user_prefs_registrar_;
+
+  // This registrar monitors for local state changes.
+  PrefChangeRegistrar local_state_registrar_;
+
+ private:
+  // Decide if we should listen for pref changes or not. If there are any
+  // JavaScript listeners registered for the onPrefsChanged event, then we
+  // want to register for change notification from the PrefChangeRegistrar.
+  // Otherwise, we want to unregister and not be listening for pref changes.
+  void StartOrStopListeningForPrefsChanges();
+
+  void OnPreferenceChanged(PrefService* service, const std::string& pref_name);
+
+  PrefChangeRegistrar* FindRegistrarForPref(const std::string& pref_name);
+
+  content::BrowserContext* context_;
+  bool listening_;
+
+  DISALLOW_COPY_AND_ASSIGN(SettingsPrivateEventRouter);
+};
+
+}  // namespace extensions
+
+#endif  // CHROME_BROWSER_EXTENSIONS_API_SETTINGS_PRIVATE_SETTINGS_PRIVATE_EVENT_ROUTER_H_