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

base/power_monitor/power_observer.h

Index: base/power_monitor/power_observer.h
diff --git a/base/power_monitor/power_observer.h b/base/power_monitor/power_observer.h
index 6be70bba9d5368dfa0cf7a4f145247a1334430ec..f9ec8b22736d601025b456e138894f103a6eb32e 100644
--- a/base/power_monitor/power_observer.h
+++ b/base/power_monitor/power_observer.h
@@ -7,14 +7,22 @@
 
 #include "base/base_export.h"
 #include "base/compiler_specific.h"
+#include "base/threading/platform_thread.h"
 
 namespace base {
 
 class BASE_EXPORT PowerObserver {
+  friend class PowerMonitor;
+
  public:
+  PowerObserver()
+      : power_monitor_thread_(0)
+  {
+  }
+
   // Notification of a change in power status of the computer, such
   // as from switching between battery and A/C power.
-  virtual void OnPowerStateChange(bool on_battery_power) {};
+  virtual void OnPowerStateChange(bool on_battery_power) {}
 
   // Notification that the system is suspending.
   virtual void OnSuspend() {}
@@ -24,6 +32,8 @@ class BASE_EXPORT PowerObserver {
 
  protected:
   virtual ~PowerObserver() {}
+
+  PlatformThreadId power_monitor_thread_;
 };
 
 }  // namespace base