Replace NULL with nullptr in all C++ files.

webrtc/voice_engine/monitor_module.cc

Index: webrtc/voice_engine/monitor_module.cc
diff --git a/webrtc/voice_engine/monitor_module.cc b/webrtc/voice_engine/monitor_module.cc
index 8a1865a95b4fc4334c020c047fda9b05d7fb03bc..2a09f4664501fb7d4673cec39f60d19e0357ffd6 100644
--- a/webrtc/voice_engine/monitor_module.cc
+++ b/webrtc/voice_engine/monitor_module.cc
@@ -15,11 +15,8 @@ namespace webrtc  {
 
 namespace voe  {
 
-MonitorModule::MonitorModule() :
-    _observerPtr(NULL),
-    _lastProcessTime(rtc::TimeMillis())
-{
-}
+MonitorModule::MonitorModule()
+    : _observerPtr(nullptr), _lastProcessTime(rtc::TimeMillis()) {}
 
 MonitorModule::~MonitorModule()
 {
@@ -45,7 +42,7 @@ MonitorModule::DeRegisterObserver()
     {
         return 0;
     }
-    _observerPtr = NULL;
+    _observerPtr = nullptr;
     return 0;
 }