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

base/power_monitor/power_observer.cc

 // Copyright 2014 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/critical_closure.h"
-
-#import <UIKit/UIKit.h>
+#include "base/power_monitor/power_observer.h"
 
 namespace base {
-namespace internal {
 
-bool IsMultiTaskingSupported() {
-  return [[UIDevice currentDevice] isMultitaskingSupported];
+PowerObserver::PowerObserver() {
 }
 
-}  // namespace internal
+PowerObserver::~PowerObserver() {
+}
+
 }  // namespace base