Replace NULL with nullptr or null in webrtc/base/.

webrtc/base/asyncsocket.h

Index: webrtc/base/asyncsocket.h
diff --git a/webrtc/base/asyncsocket.h b/webrtc/base/asyncsocket.h
index bf6c88aa391a1ec2ffd0630e48aa3da99b0ffac6..40cf1b5bd100d5a7692d8a6cd60994aff948f014 100644
--- a/webrtc/base/asyncsocket.h
+++ b/webrtc/base/asyncsocket.h
@@ -42,7 +42,7 @@ class AsyncSocket : public Socket {
 
 class AsyncSocketAdapter : public AsyncSocket, public sigslot::has_slots<> {
  public:
-  // The adapted socket may explicitly be NULL, and later assigned using Attach.
+  // The adapted socket may explicitly be null, and later assigned using Attach.
   // However, subclasses which support detached mode must override any methods
   // that will be called during the detached period (usually GetState()), to
   // avoid dereferencing a null pointer.