Replace NULL with nullptr in all C++ files.

webrtc/voice_engine/file_recorder.cc

Index: webrtc/voice_engine/file_recorder.cc
diff --git a/webrtc/voice_engine/file_recorder.cc b/webrtc/voice_engine/file_recorder.cc
index 9a0edb057ba29bb3006b9a837fa7df7bfbc164e5..9cef7968553e8af98339a6e4ef1f8a45e8f52c19 100644
--- a/webrtc/voice_engine/file_recorder.cc
+++ b/webrtc/voice_engine/file_recorder.cc
@@ -86,7 +86,7 @@ FileFormats FileRecorderImpl::RecordingFileFormat() const {
 }
 
 int32_t FileRecorderImpl::RegisterModuleFileCallback(FileCallback* callback) {
-  if (_moduleFile == NULL) {
+  if (_moduleFile == nullptr) {
     return -1;
   }
   return _moduleFile->SetModuleFileCallback(callback);
@@ -95,7 +95,7 @@ int32_t FileRecorderImpl::RegisterModuleFileCallback(FileCallback* callback) {
 int32_t FileRecorderImpl::StartRecordingAudioFile(const char* fileName,
                                                   const CodecInst& codecInst,
                                                   uint32_t notificationTimeMs) {
-  if (_moduleFile == NULL) {
+  if (_moduleFile == nullptr) {
     return -1;
   }
   codec_info_ = codecInst;