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

base/power_monitor/power_observer.cc

Index: base/power_monitor/power_observer.cc
diff --git a/base/power_monitor/power_observer.cc b/base/power_monitor/power_observer.cc
deleted file mode 100644
index 4065d6434c23b942a229e01d48f5c535f99d2cd3..0000000000000000000000000000000000000000
--- a/base/power_monitor/power_observer.cc
+++ /dev/null
@@ -1,15 +0,0 @@
-// 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/power_monitor/power_observer.h"
-
-namespace base {
-
-PowerObserver::PowerObserver() {
-}
-
-PowerObserver::~PowerObserver() {
-}
-
-}  // namespace base