Revert of Attempting to resolve a race condition with PowerMonitor

base/timer/hi_res_timer_manager_win.cc

 // Copyright (c) 2011 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.
 
 #include "base/timer/hi_res_timer_manager.h"
 
 #include "base/power_monitor/power_monitor.h"
 #include "base/time/time.h"
 
 namespace base {
 
 HighResolutionTimerManager::HighResolutionTimerManager()
     : hi_res_clock_available_(false) {
-  base::PowerMonitor::AddObserver(this);
-  UseHiResClock(!base::PowerMonitor::IsOnBatteryPower());
+  base::PowerMonitor* power_monitor = base::PowerMonitor::Get();
+  DCHECK(power_monitor != NULL);
+  power_monitor->AddObserver(this);
+  UseHiResClock(!power_monitor->IsOnBatteryPower());
 }
 
 HighResolutionTimerManager::~HighResolutionTimerManager() {
-  base::PowerMonitor::RemoveObserver(this);
+  base::PowerMonitor::Get()->RemoveObserver(this);
   UseHiResClock(false);
 }
 
 void HighResolutionTimerManager::OnPowerStateChange(bool on_battery_power) {
   UseHiResClock(!on_battery_power);
 }
 
 void HighResolutionTimerManager::UseHiResClock(bool use) {
   if (use == hi_res_clock_available_)
     return;
   hi_res_clock_available_ = use;
   base::Time::EnableHighResolutionTimer(use);
 }
 
 }  // namespace base