Check to ensure PowerObservers are added and removed on the same thread

base/power_monitor/power_monitor.cc

 // 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.
 
 #include "base/power_monitor/power_monitor.h"
+#include "base/logging.h"
 #include "base/power_monitor/power_monitor_source.h"
 
 namespace base {
 
 static PowerMonitor* g_power_monitor = NULL;
 
 PowerMonitor::PowerMonitor(scoped_ptr<PowerMonitorSource> source)
     : observers_(new ObserverListThreadSafe<PowerObserver>()),
       source_(source.Pass()) {
   DCHECK(!g_power_monitor);
   g_power_monitor = this;
 }
 
 PowerMonitor::~PowerMonitor() {
   DCHECK_EQ(this, g_power_monitor);
   g_power_monitor = NULL;
 }
 
 // static
 PowerMonitor* PowerMonitor::Get() {
   return g_power_monitor;
 }
 
 void PowerMonitor::AddObserver(PowerObserver* obs) {
+  DCHECK(!obs->power_monitor_thread_checker_);
+  obs->power_monitor_thread_checker_.reset(new base::ThreadChecker());
   observers_->AddObserver(obs);
 }
 
 void PowerMonitor::RemoveObserver(PowerObserver* obs) {
+  // PowerObservers must be removed on the same thread on which they were added.
+  DCHECK(obs->power_monitor_thread_checker_);
+  DCHECK(obs->power_monitor_thread_checker_->CalledOnValidThread());
   observers_->RemoveObserver(obs);
+  obs->power_monitor_thread_checker_.reset();
 }
 
 PowerMonitorSource* PowerMonitor::Source() {
   return source_.get();
 }
 
 bool PowerMonitor::IsOnBatteryPower() {
   return source_->IsOnBatteryPower();
 }
 
 void PowerMonitor::NotifyPowerStateChange(bool battery_in_use) {
   DVLOG(1) << "PowerStateChange: " << (battery_in_use ? "On" : "Off")
            << " battery";
   observers_->Notify(&PowerObserver::OnPowerStateChange, battery_in_use);
 }
 
 void PowerMonitor::NotifySuspend() {
   DVLOG(1) << "Power Suspending";
   observers_->Notify(&PowerObserver::OnSuspend);
 }
 
 void PowerMonitor::NotifyResume() {
   DVLOG(1) << "Power Resuming";
   observers_->Notify(&PowerObserver::OnResume);
 }
 
 }  // namespace base