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

base/power_monitor/power_monitor.cc

Index: base/power_monitor/power_monitor.cc
diff --git a/base/power_monitor/power_monitor.cc b/base/power_monitor/power_monitor.cc
index 14dc4b517832785c07153abfed2bcc4a3a738940..87ba2a656732762b1b0d50987023dc440bac8c64 100644
--- a/base/power_monitor/power_monitor.cc
+++ b/base/power_monitor/power_monitor.cc
@@ -3,6 +3,7 @@
 // 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 {
@@ -27,11 +28,16 @@ PowerMonitor* PowerMonitor::Get() {
 }
 
 void PowerMonitor::AddObserver(PowerObserver* obs) {
+  CHECK (obs->power_monitor_thread_ == 0);

[scottmg, 2014/08/25 21:43:16]

nit; no space before (

+  obs->power_monitor_thread_ = base::PlatformThread::CurrentId();
   observers_->AddObserver(obs);
 }
 
 void PowerMonitor::RemoveObserver(PowerObserver* obs) {
+  // PowerObservers must be removed on the same thread on which they were added.
+  CHECK (base::PlatformThread::CurrentId() == obs->power_monitor_thread_);

[scottmg, 2014/08/25 21:43:16]

no space, and CHECK_EQ instead

   observers_->RemoveObserver(obs);
+  obs->power_monitor_thread_ = 0;
 }
 
 PowerMonitorSource* PowerMonitor::Source() {