mus: Forward user activity from window server to detector.

ui/aura/mus/user_activity_forwarder.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 UI_AURA_MUS_USER_ACTIVITY_FORWARDER_H_
+#define UI_AURA_MUS_USER_ACTIVITY_FORWARDER_H_
+
+#include "base/compiler_specific.h"
+#include "base/macros.h"
+#include "mojo/public/cpp/bindings/binding.h"
+#include "services/ui/public/interfaces/user_activity_monitor.mojom.h"
+#include "ui/aura/aura_export.h"
+
+namespace ui {
+class UserActivityDetector;
+}
+
+namespace aura {
+
+// Helper class that receives reports of user activity from UserActivityMonitor

[James Cook, 2017/01/20 03:38:49]

super nit: I find it helpful for classes like this to document which processes
provide these interfaces. For example, this could say something like "from mojo
UserActivityMonitor interface (in the window server) to ui::UserActivityMonitor
(usually in ash)".

While this might be a "layering violation" in comments, it's super helpful for
me to figure out what is connected to what.

[Daniel Erat, 2017/01/20 16:49:45]

sure, done! i like these comments too.

+// and forwards them to ui::UserActivityDetector.
+// TODO(derat): Make current ui::UserActivityObserver implementations (i.e.
+// downstream of ui::UserActivityDetector) instead observe UserActivityMonitor
+// directly: http://crbug.com/626899
+class AURA_EXPORT UserActivityForwarder
+    : NON_EXPORTED_BASE(public ui::mojom::UserActivityObserver) {
+ public:
+  UserActivityForwarder(ui::mojom::UserActivityMonitorPtr monitor,
+                        ui::UserActivityDetector* detector);
+  ~UserActivityForwarder() override;
+
+ private:
+  // ui::mojom::UserActivityObserver:
+  void OnUserActivity() override;
+
+  ui::mojom::UserActivityMonitorPtr monitor_;
+  mojo::Binding<ui::mojom::UserActivityObserver> binding_;
+
+  ui::UserActivityDetector* detector_;  // Not owned.
+
+  DISALLOW_COPY_AND_ASSIGN(UserActivityForwarder);
+};
+
+}  // namespace aura
+
+#endif  // UI_AURA_MUS_USER_ACTIVITY_FORWARDER_H_