replace NULL->nullptr in src/remoting.

remoting/protocol/datagram_channel_factory.h

Index: remoting/protocol/datagram_channel_factory.h
diff --git a/remoting/protocol/datagram_channel_factory.h b/remoting/protocol/datagram_channel_factory.h
index 6d94ae5e256b2a84267a17e3a8b760cbf4b04f80..ae22dde23e24d2567e39465ff436a5b41bb69822 100644
--- a/remoting/protocol/datagram_channel_factory.h
+++ b/remoting/protocol/datagram_channel_factory.h
@@ -24,10 +24,11 @@ class DatagramChannelFactory {
   DatagramChannelFactory() {}
 
   // Creates new channels and calls the |callback| when then new channel is
-  // created and connected. The |callback| is called with NULL if channel setup
-  // failed for any reason. Callback may be called synchronously, before the
-  // call returns. All channels must be destroyed, and CancelChannelCreation()
-  // called for any pending channels, before the factory is destroyed.
+  // created and connected. The |callback| is called with nullptr if channel
+  // setup failed for any reason. Callback may be called synchronously, before
+  // the call returns. All channels must be destroyed, and
+  // CancelChannelCreation() called for any pending channels, before the factory
+  // is destroyed.
   virtual void CreateChannel(const std::string& name,
                              const ChannelCreatedCallback& callback) = 0;