Replace NULL with nullptr in all C++ files.

webrtc/modules/desktop_capture/screen_capturer_x11.cc

 /*
  *  Copyright (c) 2013 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 125 matching lines @@
 bool ScreenCapturerLinux::Init(const DesktopCaptureOptions& options) {
   options_ = options;
 
   root_window_ = RootWindow(display(), DefaultScreen(display()));
   if (root_window_ == BadValue) {
     LOG(LS_ERROR) << "Unable to get the root window";
     DeinitXlib();
     return false;
   }
 
-  gc_ = XCreateGC(display(), root_window_, 0, NULL);
-  if (gc_ == NULL) {
+  gc_ = XCreateGC(display(), root_window_, 0, nullptr);
+  if (gc_ == nullptr) {
     LOG(LS_ERROR) << "Unable to get graphics context";
     DeinitXlib();
     return false;
   }
 
   options_.x_display()->AddEventHandler(ConfigureNotify, this);
 
   // Check for XFixes extension. This is required for cursor shape
   // notifications, and for our use of XDamage.
   if (XFixesQueryExtension(display(), &xfixes_event_base_,
@@ skipping 251 matching lines @@
 
   std::unique_ptr<ScreenCapturerLinux> capturer(new ScreenCapturerLinux());
   if (!capturer.get()->Init(options)) {
     return nullptr;
   }
 
   return std::move(capturer);
 }
 
 }  // namespace webrtc