Cleanup usage of scoped_ptr<> in remoting for C++11

remoting/host/desktop_shape_tracker_x11.cc

 // Copyright 2013 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/desktop_shape_tracker.h"
 
 #include "base/memory/scoped_ptr.h"
 #include "third_party/webrtc/modules/desktop_capture/desktop_capture_options.h"
 
 namespace remoting {
 
 scoped_ptr<DesktopShapeTracker> DesktopShapeTracker::Create(
     webrtc::DesktopCaptureOptions options) {
-  return scoped_ptr<DesktopShapeTracker>();
+  return nullptr;
 }
 
 }  // namespace remoting