SystemMonitor refactoring: move power state monitor into a separate class called PowerMonitor

net/url_request/url_request_job.cc

Index: net/url_request/url_request_job.cc
diff --git a/net/url_request/url_request_job.cc b/net/url_request/url_request_job.cc
index 66fc9f3235687881e53b289889983641fcf9a10a..368ac96a1bf8fd51f3fe4dd58777268b73d00105 100644
--- a/net/url_request/url_request_job.cc
+++ b/net/url_request/url_request_job.cc
@@ -34,9 +34,7 @@ URLRequestJob::URLRequestJob(URLRequest* request,
       deferred_redirect_status_code_(-1),
       network_delegate_(network_delegate),
       ALLOW_THIS_IN_INITIALIZER_LIST(weak_factory_(this)) {
-  base::SystemMonitor* system_monitor = base::SystemMonitor::Get();
-  if (system_monitor)
-    base::SystemMonitor::Get()->AddPowerObserver(this);
+  base::PowerMonitor::GetInstance()->AddObserver(this);
 }
 
 void URLRequestJob::SetUpload(UploadData* upload) {
@@ -220,9 +218,7 @@ void URLRequestJob::NotifyURLRequestDestroyed() {
 }
 
 URLRequestJob::~URLRequestJob() {
-  base::SystemMonitor* system_monitor = base::SystemMonitor::Get();
-  if (system_monitor)
-    base::SystemMonitor::Get()->RemovePowerObserver(this);
+  base::PowerMonitor::GetInstance()->RemoveObserver(this);
 }
 
 void URLRequestJob::NotifyCertificateRequested(