chromeos: Add support for the battery status API on chromeos.

content/browser/battery_status/battery_status_provider_impl.cc

+// Copyright (c) 2012 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 "content/browser/battery_status/battery_status_provider_impl.h"
+
+#include "content/public/browser/power_supply_status.h"
+
+content::BatteryStatusProvider* content::BatteryStatusProvider::GetInstance() {
+  return BatteryStatusProviderImpl::GetInstance();
+}
+
+BatteryStatusProviderImpl* BatteryStatusProviderImpl::GetInstance() {
+  return Singleton<BatteryStatusProviderImpl>::get();
+}
+
+void BatteryStatusProviderImpl::AddObserver(
+    BatteryStatusProviderImpl::Observer* obs) {
+  observers_.AddObserver(obs);

[jam, 2012/04/12 19:34:55]

nit: here, and in RemoveObserver and SendUpdate, please add
DCHECK(BrowserThread::CurrentlyOn...) to ensure that this is happening on the
thread that you expect

[sadrul, 2012/04/12 21:53:24]

Done.

+}
+
+void BatteryStatusProviderImpl::RemoveObserver(
+    BatteryStatusProviderImpl::Observer* obs) {
+  observers_.RemoveObserver(obs);
+}
+
+void BatteryStatusProviderImpl::SendUpdate(
+    const content::PowerSupplyStatus& status) {
+  FOR_EACH_OBSERVER(Observer, observers_, PowerChanged(status));
+}
+
+BatteryStatusProviderImpl::BatteryStatusProviderImpl() {
+}
+
+BatteryStatusProviderImpl::~BatteryStatusProviderImpl() {
+}