Replace NULL with nullptr in webrtc/video.

webrtc/video/vie_channel.h

 /*
  *  Copyright (c) 2012 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 183 matching lines @@
   int GetRequiredNackListSize(int target_delay_ms);
 
   // ViEChannel exposes methods that allow to modify observers and callbacks
   // to be modified. Such an API-style is cumbersome to implement and maintain
   // at all the levels when comparing to only setting them at construction. As
   // so this class instantiates its children with a wrapper that can be modified
   // at a later time.
   template <class T>
   class RegisterableCallback : public T {
    public:
-    RegisterableCallback() : callback_(NULL) {}
+    RegisterableCallback() : callback_(nullptr) {}
 
     void Set(T* callback) {
       rtc::CritScope lock(&critsect_);
       callback_ = callback;
     }
 
    protected:
     // Note: this should be implemented with a RW-lock to allow simultaneous
     // calls into the callback. However that doesn't seem to be needed for the
     // current type of callbacks covered by this class.
@@ skipping 87 matching lines @@
 
   int64_t last_rtt_ms_ GUARDED_BY(crit_);
 
   // RtpRtcp modules, declared last as they use other members on construction.
   const std::vector<RtpRtcp*> rtp_rtcp_modules_;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_VIDEO_VIE_CHANNEL_H_