Replace NULL with nullptr in all C++ files.

webrtc/test/testsupport/trace_to_stderr.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 19 matching lines @@
 
 TraceToStderr::TraceToStderr(bool override_time)
     : override_time_(override_time),
       time_seconds_(0) {
   Trace::set_level_filter(kLevelFilter);
   Trace::CreateTrace();
   Trace::SetTraceCallback(this);
 }
 
 TraceToStderr::~TraceToStderr() {
-  Trace::SetTraceCallback(NULL);
+  Trace::SetTraceCallback(nullptr);
   Trace::ReturnTrace();
 }
 
 void TraceToStderr::SetTimeSeconds(float time) { time_seconds_ = time; }
 
 void TraceToStderr::Print(TraceLevel level, const char* msg_array, int length) {
   if (level & kLevelFilter) {
     assert(length > Trace::kBoilerplateLength);
     std::string msg = msg_array;
     std::string msg_log = msg.substr(Trace::kBoilerplateLength);
     if (override_time_) {
       fprintf(stderr, "%.2fs %s\n", time_seconds_, msg_log.c_str());
     } else {
       std::string msg_time = msg.substr(Trace::kTimestampPosition,
                                         Trace::kTimestampLength);
       fprintf(stderr, "%s %s\n", msg_time.c_str(), msg_log.c_str());
     }
     fflush(stderr);
   }
 }
 
 }  // namespace test
 }  // namespace webrtc