Replace NULL with nullptr in all C++ files.

webrtc/base/asyncinvoker.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 12 matching lines @@
   // Messages for this need to be cleared *before* our destructor is complete.
   MessageQueueManager::Clear(this);
 }
 
 void AsyncInvoker::OnMessage(Message* msg) {
   // Get the AsyncClosure shared ptr from this message's data.
   ScopedRefMessageData<AsyncClosure>* data =
       static_cast<ScopedRefMessageData<AsyncClosure>*>(msg->pdata);
   scoped_refptr<AsyncClosure> closure = data->data();
   delete msg->pdata;
-  msg->pdata = NULL;
+  msg->pdata = nullptr;
 
   // Execute the closure and trigger the return message if needed.
   closure->Execute();
 }
 
 void AsyncInvoker::Flush(Thread* thread, uint32_t id /*= MQID_ANY*/) {
   if (destroying_) return;
 
   // Run this on |thread| to reduce the number of context switches.
   if (Thread::Current() != thread) {
@@ skipping 81 matching lines @@
     invoker_->AsyncInvoke<void>(callback_posted_from_, calling_thread_,
                                 callback_);
   }
 }
 
 void NotifyingAsyncClosureBase::CancelCallback() {
   // If the callback is triggering when this is called, block the
   // destructor of the dying object here by waiting until the callback
   // is done triggering.
   CritScope cs(&crit_);
-  // calling_thread_ == NULL means do not trigger the callback.
-  calling_thread_ = NULL;
+  // calling_thread_ == null means do not trigger the callback.
+  calling_thread_ = nullptr;
 }
 
 }  // namespace rtc