Record the fraction of the time without user input - Aura only

ui/events/fraction_of_time_without_user_input_recorder.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_EVENTS_IDLE_FRACTION_RECORDER_H_
+#define UI_EVENTS_IDLE_FRACTION_RECORDER_H_
+
+#include "base/time/time.h"
+#include "ui/events/events_base_export.h"
+
+namespace ui {
+
+// Receives as input a set of timestamps indicating when events were
+// received. Reports via UMA the fraction of the time per |window_size_| that
+// the user was interacting.
+class EVENTS_BASE_EXPORT FractionOfTimeWithoutUserInputRecorder {
+ public:
+  FractionOfTimeWithoutUserInputRecorder();
+  void RecordEventAtTime(base::TimeTicks start_time);
+
+ protected:
+  // We report the fraction of the time we were idle once per |window_size_|.
+  base::TimeDelta window_size_;
+
+  // Two events within |idle_timeout_| of one another are considered to be in
+  // the same period of user activity.
+  base::TimeDelta idle_timeout_;

[sadrul, 2017/03/19 00:38:51]

Move to private, add protected accessors instead.

[tdresser, 2017/03/24 14:56:31]

I'm modifying these from the unit test (to keep our tests from failing when we
tweak these constants).

To make these members private, I'd need to add protected getters & setters, and
then expose the getters publicly on TestFractionOfTimeWithoutUserInputRecorder,
which feels like a lot of overhead for very little value.

Do you think this is worth doing?

[sadrul, 2017/03/24 17:29:33]

I don't really care strongly either way. (although I think the style-guide did
not/does not have an exception for this)

[tdresser, 2017/03/27 18:59:26]

Done.

+
+  virtual void RecordActiveInterval(base::TimeTicks start_time,
+                                    base::TimeTicks end_time);
+
+  virtual void RecordToUma(float idle_fraction);
+
+ private:
+  // Within the current period of length |window_size_|, how long has the user
+  // been active?
+  base::TimeDelta current_window_active_time_;
+  // If the user is currently active, when did they start being active?
+  base::TimeTicks active_duration_start_time_;
+  base::TimeTicks window_start_time_;
+  base::TimeTicks previous_event_end_time_;
+};
+
+}  // namespace ui
+
+#endif  // UI_EVENTS_IDLE_FRACTION_RECORDER_H_