Fix compilation issues of std::unique_ptr

webrtc/p2p/base/transportdescription.h

Index: webrtc/p2p/base/transportdescription.h
diff --git a/webrtc/p2p/base/transportdescription.h b/webrtc/p2p/base/transportdescription.h
index e7f9263b3e2ff29981183f44ab9e33b7c7e88736..6f4e9a4bf171137a6cd11bee8f814cc961ba5f70 100644
--- a/webrtc/p2p/base/transportdescription.h
+++ b/webrtc/p2p/base/transportdescription.h
@@ -147,7 +147,7 @@ struct TransportDescription {
   void AddOption(const std::string& option) {
     transport_options.push_back(option);
   }
-  bool secure() const { return identity_fingerprint != NULL; }
+  bool secure() const { return identity_fingerprint != nullptr; }
 
   IceParameters GetIceParameters() {
     return IceParameters(ice_ufrag, ice_pwd, HasOption(ICE_RENOMINATION_STR));