Battery impact UMA

content/browser/power_usage_monitor_impl.h

+// Copyright 2014 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_CONTENT_BROWSER_POWER_USAGE_MONITOR_IMPL_H_
+#define CHROME_CONTENT_BROWSER_POWER_USAGE_MONITOR_IMPL_H_
+
+#include "base/basictypes.h"
+#include "base/containers/hash_tables.h"
+#include "base/gtest_prod_util.h"
+#include "base/memory/singleton.h"
+#include "base/power_monitor/power_monitor.h"
+#include "base/time/time.h"
+#include "content/browser/battery_status/battery_status_service.h"

[timvolodine, 2014/10/28 23:44:03]

note that battery API has recently been moved to device/battery, see
https://codereview.chromium.org/685703002/.

[jeremy, 2014/11/02 15:06:21]

Done.

+#include "content/public/browser/browser_message_filter.h"
+#include "content/public/browser/notification_observer.h"
+#include "content/public/browser/notification_registrar.h"
+#include "third_party/WebKit/public/platform/WebBatteryStatus.h"

[Daniel Erat, 2014/10/27 16:15:58]

it feels strange to have content/ depend on blink for the battery status,
considering that blink depends on content/ to get it in the first place (from my
reading of e.g. https://codereview.chromium.org/356873002). all of this seems
like it ought to be coming from base/power_monitor/ in the first place instead
of having yet another implementation in content/. (the base code would need to
be updated to also include the battery level, though.)

[sadrul, 2014/10/27 20:57:39]

We have similar issues for events too, where we convert from ui::Event to
blink::WebInputEvent in content/ before handing it over to blink.
+timvolodine@

[timvolodine, 2014/10/28 23:44:03]

as noted above after the move to device/battery we now have a BatteryStatus
class there (i.e. from battery_status.mojom). in the longer term the
WebBatteryStatus may be merged when blink and chromium repositories merge...

+
+namespace content {
+
+// Record statistics on power usage.
+//
+// Two main statics are recorded by this class:
+// * Power.BatteryDischarge_{5,15,30} - delta between battery level when
+//   unplugged from wallpower, over the specified period - in minutes.
+// * Power.BatteryDischargeRateWhenUnplugged - the rate of battery discharge
+//   from the device being unplugged until it's plugged back in, if said period
+//   was longer than 30 minutes.
+//
+// Heuristics:
+// * Metrics are only collected once per day.
+// * If the machine goes to sleep or all renderers are closed then the current
+//   measurement is cancelled.
+class PowerUsageMonitor : public base::PowerObserver,
+                          public NotificationObserver {
+ public:
+  class SystemInterface {
+   public:
+    virtual ~SystemInterface() {}
+
+    virtual void ScheduleHistogramReport(base::TimeDelta delay) = 0;
+    virtual void CancelPendingHistogramReports() = 0;
+
+    // Allow tests to override clock.
+    virtual base::Time Now() = 0;
+
+   protected:
+    virtual void ReportBatteryLevelHistogram(

[Daniel Erat, 2014/10/27 16:15:58]

it doesn't make sense to me to declare a private or protected method in an
interface. why not just let the implementations handle this themselves?

[jeremy, 2014/11/02 15:06:21]

Done.

+        base::Time start_time,
+        base::TimeDelta discharge_time) = 0;
+  };
+
+ public:
+  PowerUsageMonitor();
+  virtual ~PowerUsageMonitor();
+
+  // Start monitoring power usage.
+  void Start();
+
+  double discharge_amount() {
+    return initial_battery_level_ - current_battery_level_;
+  }
+
+  // Called by SystemInterface after a histogram was succesfully recorded.
+  void BatteryLevelReported();
+
+  void SetSystemInterfaceForTest(scoped_ptr<SystemInterface> interface);
+  void SetRenderersForTest(bool has_live_renderers);
+
+  // Overridden from base::PowerObserver:
+  void OnPowerStateChange(bool on_battery_power) override {};
+  void OnResume() override {};
+  void OnSuspend() override;
+
+  // Overridden from NotificationObserver:
+  void Observe(int type,
+               const NotificationSource& source,
+               const NotificationDetails& details) override;
+
+ private:
+  friend class PowerUsageMonitorTest;
+  FRIEND_TEST_ALL_PREFIXES(PowerUsageMonitorTest, OnBatteryStatusUpdate);
+
+  void StartOnIOThread();
+
+  void OnBatteryStatusUpdate(const blink::WebBatteryStatus& status);
+
+  void DischargeStarted(double battery_level);
+  void WallPowerConnected(double battery_level);
+
+  void CancelPendingHistogramReporting();
+
+  BatteryStatusService::BatteryUpdateCallback callback_;
+  scoped_ptr<BatteryStatusService::BatteryUpdateSubscription> subscription_;
+
+  NotificationRegistrar registrar_;
+
+  scoped_ptr<SystemInterface> system_interface_;
+
+  // True if monitoring was started (Start() called).
+  bool started_;
+
+  // True if the system is running on battery power, false if on wall power.
+  bool on_battery_power_;
+
+  // Battery level when wall power disconnected, 0 if on wall power.
+  double initial_battery_level_;

[Daniel Erat, 2014/10/27 16:15:58]

document the scale for this. looking at the docs for the api that blink is
implementing, it seems like it's [0.0, 1.0], where 1.0 indicates a full battery.

[jeremy, 2014/11/02 15:06:21]

Done.

+
+  // Current battery level, 0 if on wall power.
+  double current_battery_level_;
+
+  // Timestamp when wall power was disconnected, null Time object otherwise.
+  base::Time start_discharge_time_;
+
+  // Timestamp for when the first histogram is reported in a 24 hour period.
+  // Used for rate-limiting.
+  base::Time first_histogram_report_time_;
+
+  // IDs of live renderer processes.
+  base::hash_set<int> live_renderer_ids_;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(PowerUsageMonitor);
+};
+
+}  // namespace content
+
+#endif  // CHROME_CONTENT_BROWSER_POWER_USAGE_MONITOR_IMPL_H_