Make SystemMonitor not a Singleton and move it out of base

app/hi_res_timer_manager_win.cc

+// Copyright (c) 2009 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 "app/hi_res_timer_manager.h"
+
+#include "base/time.h"
+
+HighResolutionTimerManager::HighResolutionTimerManager()
+    : hi_res_clock_used_(false) {
+  SystemMonitor* system_monitor = SystemMonitor::Get();
+  system_monitor->AddObserver(this);
+  UseHiResClock(!system_monitor->BatteryPower());
+}
+
+HighResolutionTimerManager::~HighResolutionTimerManager() {
+  SystemMonitor::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_used_)
+    return;
+  bool result = base::Time::UseHighResolutionTimer(use);
+  DCHECK(result);
+  hi_res_clock_used_ = use;
+}