Replace NULL with nullptr or null in webrtc/api/.

webrtc/api/notifier.h

 /*
  *  Copyright 2011 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.
  */
 
 #ifndef WEBRTC_API_NOTIFIER_H_
 #define WEBRTC_API_NOTIFIER_H_
 
 #include <list>
 
 #include "webrtc/api/mediastreaminterface.h"
 #include "webrtc/base/checks.h"
 
 namespace webrtc {
 
 // Implements a template version of a notifier.
 // TODO(deadbeef): This is an implementation detail; move out of api/.
 template <class T>
 class Notifier : public T {
  public:
   Notifier() {
   }
 
   virtual void RegisterObserver(ObserverInterface* observer) {
-    RTC_DCHECK(observer != NULL);
+    RTC_DCHECK(observer != nullptr);
     observers_.push_back(observer);
   }
 
   virtual void UnregisterObserver(ObserverInterface* observer) {
     for (std::list<ObserverInterface*>::iterator it = observers_.begin();
          it != observers_.end(); it++) {
       if (*it == observer) {
         observers_.erase(it);
         break;
       }
@@ skipping 11 matching lines @@
     }
   }
 
  protected:
   std::list<ObserverInterface*> observers_;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_API_NOTIFIER_H_