Extract kArcEnabled preference from ArcSessionManager part 2.

chrome/browser/chromeos/arc/arc_play_store_enabled_preference_handler.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 CHROME_BROWSER_CHROMEOS_ARC_ARC_PLAY_STORE_ENABLED_PREFERENCE_HANDLER_H_
+#define CHROME_BROWSER_CHROMEOS_ARC_ARC_PLAY_STORE_ENABLED_PREFERENCE_HANDLER_H_
+
+#include "base/macros.h"
+#include "base/memory/weak_ptr.h"
+#include "components/prefs/pref_change_registrar.h"
+#include "components/sync_preferences/pref_service_syncable_observer.h"
+
+class Profile;

[Yusuke Sato, 2017/03/01 18:09:26]

nit: As you know,
https://google.github.io/styleguide/cppguide.html#Forward_Declarations says "Try
to avoid forward declarations of entities defined in another project." Do you
know what "another project" usually means in Chromium? Depending on the
definition, we probably should start reducing forward declarations in new files.

[hidehiko, 2017/03/01 19:21:31]

AFAIK, in Chromium, the rule is overriden by
https://chromium.googlesource.com/chromium/src/+/master/styleguide/c++/c++.md...

[Luis Héctor Chávez, 2017/03/02 00:09:17]

Yes, Chromium is considered to be a single project :)

+
+namespace arc {
+
+class ArcSessionManager;
+
+// Observes Google Play Store enabled preference (whose key is "arc.enabled"
+// for historical reason), and controls ARC via ArcSessionManager.
+// In addition, this controls showing/hiding a notification to enable Google
+// Play Store.
+class ArcPlayStoreEnabledPreferenceHandler
+    : public sync_preferences::PrefServiceSyncableObserver {
+ public:
+  ArcPlayStoreEnabledPreferenceHandler(Profile* profile,
+                                       ArcSessionManager* arc_session_manager);
+  ~ArcPlayStoreEnabledPreferenceHandler() override;
+
+  // Starts observing Google Play Store enabled preference change.
+  // Also, based on its initial value, this may start ArcSession, or may start
+  // removing the data, as initial state.
+  // In addition, this triggers to show ArcAuthNotification, if necessary.
+  void Start();
+
+ private:
+  // Called when Google Play Store enabled preference is changed.
+  void OnPreferenceChanged();
+
+  // sync_preferences::PrefServiceSyncableObserver:
+  void OnIsSyncingChanged() override;
+
+  Profile* const profile_;
+
+  // Owned by ArcServiceLauncher.
+  ArcSessionManager* const arc_session_manager_;
+
+  // Registrar used to monitor ARC enabled state.
+  PrefChangeRegistrar pref_change_registrar_;
+
+  // Must be the last member.
+  base::WeakPtrFactory<ArcPlayStoreEnabledPreferenceHandler> weak_ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(ArcPlayStoreEnabledPreferenceHandler);
+};
+
+}  // namespace arc
+
+#endif  // CHROME_BROWSER_CHROMEOS_ARC_ARC_PLAY_STORE_ENABLED_PREFERENCE_HANDLER_H_