Implement base::PowerMonitor::IsOnBatteryPower() for OSX.

base/power_monitor/power_monitor_device_source.h

 // Copyright 2013 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 BASE_POWER_MONITOR_POWER_MONITOR_DEVICE_SOURCE_H_
 #define BASE_POWER_MONITOR_POWER_MONITOR_DEVICE_SOURCE_H_
 
 #include "base/base_export.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/observer_list_threadsafe.h"
 #include "base/power_monitor/power_monitor_source.h"
 #include "base/power_monitor/power_observer.h"
 #include "build/build_config.h"
 
 #if defined(OS_WIN)
 #include <windows.h>
-
-// Windows HiRes timers drain the battery faster so we need to know the battery
-// status.  This isn't true for other platforms.
-#define ENABLE_BATTERY_MONITORING 1
-#else
-#undef ENABLE_BATTERY_MONITORING
 #endif  // !OS_WIN
 
-#if defined(ENABLE_BATTERY_MONITORING)
-#include "base/timer/timer.h"
-#endif  // defined(ENABLE_BATTERY_MONITORING)
-
 #if defined(OS_IOS)
 #include <objc/runtime.h>
 #endif  // OS_IOS
 
 namespace base {
 
 // A class used to monitor the power state change and notify the observers about
 // the change event.
 class BASE_EXPORT PowerMonitorDeviceSource : public PowerMonitorSource {

[Robert Sesek, 2016/09/26 22:21:19]

This class has kind of a weird design with all the platform-specific #ifs. It
seems like each platform should get to define its own version of
PowerMonitorDeviceSource (like base/memory/memory_pressure_monitor.h does). But
that's outside the scope of this CL.

  public:
   PowerMonitorDeviceSource();
   ~PowerMonitorDeviceSource() override;
 
 #if defined(OS_MACOSX)
   // Allocate system resources needed by the PowerMonitor class.
   //
   // This function must be called before instantiating an instance of the class
   // and before the Sandbox is initialized.
 #if !defined(OS_IOS)
@@ skipping 35 matching lines @@
 #endif  // OS_WIN
 
 #if defined(OS_MACOSX)
   void PlatformInit();
   void PlatformDestroy();
 #endif
 
   // Platform-specific method to check whether the system is currently
   // running on battery power.  Returns true if running on batteries,
   // false otherwise.
   bool IsOnBatteryPowerImpl() override;

[Nico, 2016/09/27 20:59:33]

Ah, because this is in the vtable. But what references the vtable?

...probably this
https://cs.chromium.org/chromium/src/ios/web/app/web_main_loop.mm?rcl=0&l=75

So now we're in a situation where the function isn't implemented, but we have a
stub. I guess Rohit figured it's not super important, so landing this as-is
seems fine, but we should probably delete that ref (not in this Cl, and not you)
and then the ios implementation of the empty function, so that if someone
actually wants to use it they'll get a linker error informing them they need to
implement it.

 
-  // Checks the battery status and notifies observers if the battery
-  // status has changed.
-  void BatteryCheck();
-
 #if defined(OS_IOS)
   // Holds pointers to system event notification observers.
   std::vector<id> notification_observers_;
 #endif
 
-#if defined(ENABLE_BATTERY_MONITORING)
-  base::OneShotTimer delayed_battery_check_;
-#endif
-
 #if defined(OS_WIN)
   PowerMessageWindow power_message_window_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(PowerMonitorDeviceSource);
 };
 
 }  // namespace base
 
 #endif  // BASE_POWER_MONITOR_POWER_MONITOR_DEVICE_SOURCE_H_