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

webrtc/base/timeutils.cc

 /*
  *  Copyright 2004 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 171 matching lines @@
 
   // Combine all variables into seconds from 1970-01-01 00:00 (except |month|
   // which was accumulated into |day| above).
   return (((static_cast<int64_t>
             (year - 1970) * 365 + day) * 24 + hour) * 60 + min) * 60 + sec;
 }
 
 int64_t TimeUTCMicros() {
 #if defined(WEBRTC_POSIX)
   struct timeval time;
-  gettimeofday(&time, NULL);
+  gettimeofday(&time, nullptr);
   // Convert from second (1.0) and microsecond (1e-6).
   return (static_cast<int64_t>(time.tv_sec) * rtc::kNumMicrosecsPerSec +
           time.tv_usec);
 
 #elif defined(WEBRTC_WIN)
   struct _timeb time;
   _ftime(&time);
   // Convert from second (1.0) and milliseconds (1e-3).
   return (static_cast<int64_t>(time.time) * rtc::kNumMicrosecsPerSec +
           static_cast<int64_t>(time.millitm) * rtc::kNumMicrosecsPerMillisec);
 #endif
 }
 
 } // namespace rtc