Make SystemMonitor not a Singleton and move it out of base

app/hi_res_timer_manager_posix.cc

Index: app/hi_res_timer_manager_posix.cc
diff --git a/app/hi_res_timer_manager_posix.cc b/app/hi_res_timer_manager_posix.cc
new file mode 100644
index 0000000000000000000000000000000000000000..f0562fd1c8c5096f5236fc4c262cb4f9ffd6d8e3
--- /dev/null
+++ b/app/hi_res_timer_manager_posix.cc
@@ -0,0 +1,19 @@
+// 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"
+
+// On POSIX we don't need to do anything special with the system timer.
+
+HighResolutionTimerManager::HighResolutionTimerManager() {
+}
+
+HighResolutionTimerManager::~HighResolutionTimerManager() {
+}
+
+void HighResolutionTimerManager::OnPowerStateChange(bool on_battery_power) {
+}
+
+void HighResolutionTimerManager::UseHiResClock(bool use) {
+}