Add watch time metrics for HTML5 media playback.

media/blink/watch_time_reporter.h

Index: media/blink/watch_time_reporter.h
diff --git a/media/blink/watch_time_reporter.h b/media/blink/watch_time_reporter.h
new file mode 100644
index 0000000000000000000000000000000000000000..5b1e436c0174f328430931e666066687172f8ef0
--- /dev/null
+++ b/media/blink/watch_time_reporter.h
@@ -0,0 +1,98 @@
+// Copyright 2016 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 MEDIA_BLINK_WATCH_TIME_REPORTER_H_
+#define MEDIA_BLINK_WATCH_TIME_REPORTER_H_
+
+#include "base/callback.h"
+#include "base/power_monitor/power_observer.h"
+#include "base/time/time.h"
+#include "base/timer/timer.h"
+#include "media/base/timestamp_constants.h"
+#include "media/blink/media_blink_export.h"
+#include "ui/gfx/geometry/size.h"
+
+namespace media {
+
+class MEDIA_BLINK_EXPORT WatchTimeReporter : base::PowerObserver {
+ public:
+  using GetMediaTimeCB = base::Callback<base::TimeDelta(void)>;
+  WatchTimeReporter(bool has_audio,
+                    bool has_video,
+                    bool is_mse,
+                    bool is_encrypted,
+                    const gfx::Size& initial_video_size,
+                    const GetMediaTimeCB& get_media_time_cb);
+  ~WatchTimeReporter() override;
+
+  void OnPlaying();
+  void OnPaused();
+  void OnSeeking(base::TimeDelta seek_timestamp);
+  void OnVolumeChange(double volume);
+  void OnShown();
+  void OnHidden();
+
+ private:
+  friend class WatchTimeReporterTest;
+
+  // Histogram names used for reporting. Exported for testing purposes only.
+  static const char kHistogramAudioVideoAll[];
+  static const char kHistogramAudioVideoMse[];
+  static const char kHistogramAudioVideoEme[];
+  static const char kHistogramAudioVideoSrc[];
+  static const char kHistogramAudioVideoBattery[];
+  static const char kHistogramAudioVideoAc[];
+
+  // base::PowerObserver implementation.
+  //
+  // We only observe power source changes. We don't need to observe suspend and
+  // resume events because we report watch time in terms of elapsed media time
+  // and not in terms of elapsed real time.
+  void OnPowerStateChange(bool on_battery_power) override;
+
+  bool ShouldReportWatchTime();
+  void StartReportingTimer(base::TimeDelta start_timestamp);
+  enum class FinalizeTime { IMMEDIATELY, ON_NEXT_UPDATE };
+  void FinalizeWatchTime(FinalizeTime finalize_time);
+  void UpdateWatchTime();
+
+  // Initialized during construction.
+  const bool has_audio_;
+  const bool has_video_;
+  const bool is_mse_;
+  const bool is_encrypted_;
+  const gfx::Size initial_video_size_;
+  const GetMediaTimeCB get_media_time_cb_;
+
+  // The amount of time between each UpdateWatchTime(); this is the frequency by
+  // which the histograms are updated. In the event of a process crash or kill
+  // this is also the most amount of watch time that we might lose.
+  base::TimeDelta reporting_interval_ = base::TimeDelta::FromSeconds(5);
+
+  base::RepeatingTimer reporting_timer_;
+
+  // Updated by the OnXXX() methods above.
+  bool is_on_battery_power_ = false;
+  bool is_playing_ = false;
+  bool is_visible_ = true;
+  double volume_ = 1.0;
+
+  // The last media timestamp seen by UpdateWatchTime().
+  base::TimeDelta last_media_timestamp_ = kNoTimestamp;
+
+  // The starting and ending timestamps used for reporting watch time.
+  base::TimeDelta start_timestamp_;
+  base::TimeDelta end_timestamp_ = kNoTimestamp;
+
+  // Similar to the above but tracks watch time relative to whether or not
+  // battery or AC power is being used.
+  base::TimeDelta start_timestamp_for_power_;
+  base::TimeDelta end_timestamp_for_power_ = kNoTimestamp;
+
+  DISALLOW_COPY_AND_ASSIGN(WatchTimeReporter);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BLINK_WATCH_TIME_REPORTER_H_