replace NULL->nullptr in src/remoting.

remoting/host/client_session.cc

Index: remoting/host/client_session.cc
diff --git a/remoting/host/client_session.cc b/remoting/host/client_session.cc
index d86c955afabf38d031baef680f27a9c82313dba4..1b580dc8370e8bea4964d32816d75d82b471335c 100644
--- a/remoting/host/client_session.cc
+++ b/remoting/host/client_session.cc
@@ -136,7 +136,7 @@ void ClientSession::NotifyClientResolution(
 void ClientSession::ControlVideo(const protocol::VideoControl& video_control) {
   DCHECK(CalledOnValidThread());
 
-  // Note that |video_scheduler_| may be NULL, depending upon whether extensions
+  // Note that |video_scheduler_| may be null, depending upon whether extensions
   // choose to wrap or "steal" the video capturer or encoder.
   if (video_control.has_enable()) {
     VLOG(1) << "Received VideoControl (enable="
@@ -366,11 +366,11 @@ void ClientSession::OnConnectionClosed(
   // longer valid once ConnectionToClient calls OnConnectionClosed().
   if (audio_scheduler_.get()) {
     audio_scheduler_->Stop();
-    audio_scheduler_ = NULL;
+    audio_scheduler_ = nullptr;
   }
   if (video_scheduler_.get()) {
     video_scheduler_->Stop();
-    video_scheduler_ = NULL;
+    video_scheduler_ = nullptr;
   }
 
   client_clipboard_factory_.InvalidateWeakPtrs();
@@ -436,7 +436,7 @@ void ClientSession::ResetVideoPipeline() {
 
   if (video_scheduler_.get()) {
     video_scheduler_->Stop();
-    video_scheduler_ = NULL;
+    video_scheduler_ = nullptr;
   }
 
   // Create VideoEncoder and DesktopCapturer to match the session's video