Replace NULL with nullptr in all C++ files.

webrtc/api/statstypes.cc

 /*
  *  Copyright 2014 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 761 matching lines @@
       [&id](const StatsReport* r)->bool { return r->id()->Equals(id); });
   if (it != end()) {
     StatsReport* report = new StatsReport((*it)->id());
     delete *it;
     *it = report;
     return report;
   }
   return InsertNew(id);
 }
 
-// Looks for a report with the given |id|.  If one is not found, NULL
+// Looks for a report with the given |id|.  If one is not found, null
 // will be returned.
 StatsReport* StatsCollection::Find(const StatsReport::Id& id) {
   RTC_DCHECK(thread_checker_.CalledOnValidThread());
   Container::iterator it = std::find_if(list_.begin(), list_.end(),
       [&id](const StatsReport* r)->bool { return r->id()->Equals(id); });
   return it == list_.end() ? nullptr : *it;
 }
 
 }  // namespace webrtc