SystemMonitor refactoring: move power state monitor into a separate class called PowerMonitor

base/hi_res_timer_manager_win.cc

Index: base/hi_res_timer_manager_win.cc
diff --git a/base/hi_res_timer_manager_win.cc b/base/hi_res_timer_manager_win.cc
index 1a9239449473490059443025b8957f1bf62803b3..5bb4791b99106196b1da2299cf9f7f50184c649d 100644
--- a/base/hi_res_timer_manager_win.cc
+++ b/base/hi_res_timer_manager_win.cc
@@ -8,13 +8,13 @@
 
 HighResolutionTimerManager::HighResolutionTimerManager()
     : hi_res_clock_available_(false) {
-  base::SystemMonitor* system_monitor = base::SystemMonitor::Get();
-  system_monitor->AddPowerObserver(this);
-  UseHiResClock(!system_monitor->BatteryPower());
+  base::PowerMonitor* power_monitor = base::PowerMonitor::GetInstance();
+  power_monitor->AddObserver(this);
+  UseHiResClock(!power_monitor->BatteryPower());
 }
 
 HighResolutionTimerManager::~HighResolutionTimerManager() {
-  base::SystemMonitor::Get()->RemovePowerObserver(this);
+  base::PowerMonitor::GetInstance()->RemoveObserver(this);
   UseHiResClock(false);
 }