Replace NULL with nullptr in all C++ files.

webrtc/voice_engine/voe_audio_processing_impl.cc

Index: webrtc/voice_engine/voe_audio_processing_impl.cc
diff --git a/webrtc/voice_engine/voe_audio_processing_impl.cc b/webrtc/voice_engine/voe_audio_processing_impl.cc
index 3ee0e9562fd7c4793948cc2830e9861a251dc9da..9e0437421feb363c83ee601ff02a674043df27fc 100644
--- a/webrtc/voice_engine/voe_audio_processing_impl.cc
+++ b/webrtc/voice_engine/voe_audio_processing_impl.cc
@@ -44,8 +44,8 @@ static const EcModes kDefaultEcMode = kEcAec;
 #endif
 
 VoEAudioProcessing* VoEAudioProcessing::GetInterface(VoiceEngine* voiceEngine) {
-  if (NULL == voiceEngine) {
-    return NULL;
+  if (nullptr == voiceEngine) {
+    return nullptr;
   }
   VoiceEngineImpl* s = static_cast<VoiceEngineImpl*>(voiceEngine);
   s->AddRef();
@@ -524,7 +524,7 @@ int VoEAudioProcessingImpl::VoiceActivityIndicator(int channel) {
 
   voe::ChannelOwner ch = _shared->channel_manager().GetChannel(channel);
   voe::Channel* channelPtr = ch.channel();
-  if (channelPtr == NULL) {
+  if (channelPtr == nullptr) {
     _shared->SetLastError(VE_CHANNEL_NOT_VALID, kTraceError,
                           "VoiceActivityIndicator() failed to locate channel");
     return -1;