replace NULL->nullptr in src/remoting.

remoting/host/ipc_mouse_cursor_monitor.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 "remoting/host/ipc_mouse_cursor_monitor.h"
 
 #include "remoting/host/desktop_session_proxy.h"
 #include "third_party/webrtc/modules/desktop_capture/mouse_cursor.h"
 
 namespace remoting {
 
 IpcMouseCursorMonitor::IpcMouseCursorMonitor(
     scoped_refptr<DesktopSessionProxy> desktop_session_proxy)
-    : callback_(NULL),
+    : callback_(nullptr),
       desktop_session_proxy_(desktop_session_proxy),
       weak_factory_(this) {
 }
 
 IpcMouseCursorMonitor::~IpcMouseCursorMonitor() {}
 
 void IpcMouseCursorMonitor::Init(Callback* callback, Mode mode) {
   DCHECK(!callback_);
   DCHECK(callback);
   DCHECK_EQ(webrtc::MouseCursorMonitor::SHAPE_ONLY, mode);
   callback_ = callback;
   desktop_session_proxy_->SetMouseCursorMonitor(weak_factory_.GetWeakPtr());
 }
 
 void IpcMouseCursorMonitor::Capture() {
   // Ignore. DesktopSessionAgent will capture the cursor at the same time it
   // captures a screen frame when |IpcVideoFrameCapturer::Capture()| is called.
   // This saves an IPC roundtrip.
 }
 
 void IpcMouseCursorMonitor::OnMouseCursor(
     scoped_ptr<webrtc::MouseCursor> cursor) {
   DCHECK(callback_);
   callback_->OnMouseCursor(cursor.release());
 }
 
 }  // namespace remoting