Replace NULL with nullptr in all C++ files.

webrtc/system_wrappers/source/condition_variable_event_win.cc

Index: webrtc/system_wrappers/source/condition_variable_event_win.cc
diff --git a/webrtc/system_wrappers/source/condition_variable_event_win.cc b/webrtc/system_wrappers/source/condition_variable_event_win.cc
index 535cbc5460f7c9eca49fe93df0d040ab86223be0..9ed5333819a790c24fc551898ecffbc6fca287f9 100644
--- a/webrtc/system_wrappers/source/condition_variable_event_win.cc
+++ b/webrtc/system_wrappers/source/condition_variable_event_win.cc
@@ -94,20 +94,20 @@ ConditionVariableEventWin::ConditionVariableEventWin() : eventID_(WAKEALL_0) {
 
   InitializeCriticalSection(&num_waiters_crit_sect_);
 
-  events_[WAKEALL_0] = CreateEvent(NULL,  // no security attributes
-                                   TRUE,  // manual-reset, sticky event
-                                   FALSE,  // initial state non-signaled
-                                   NULL);  // no name for event
-
-  events_[WAKEALL_1] = CreateEvent(NULL,  // no security attributes
-                                   TRUE,  // manual-reset, sticky event
-                                   FALSE,  // initial state non-signaled
-                                   NULL);  // no name for event
-
-  events_[WAKE] = CreateEvent(NULL,  // no security attributes
-                              FALSE,  // auto-reset, sticky event
-                              FALSE,  // initial state non-signaled
-                              NULL);  // no name for event
+  events_[WAKEALL_0] = CreateEvent(nullptr,   // no security attributes
+                                   TRUE,      // manual-reset, sticky event
+                                   FALSE,     // initial state non-signaled
+                                   nullptr);  // no name for event
+
+  events_[WAKEALL_1] = CreateEvent(nullptr,   // no security attributes
+                                   TRUE,      // manual-reset, sticky event
+                                   FALSE,     // initial state non-signaled
+                                   nullptr);  // no name for event
+
+  events_[WAKE] = CreateEvent(nullptr,   // no security attributes
+                              FALSE,     // auto-reset, sticky event
+                              FALSE,     // initial state non-signaled
+                              nullptr);  // no name for event
 }
 
 ConditionVariableEventWin::~ConditionVariableEventWin() {