Added a virtual destructor to get the test to compile on all platforms.

BUG=
TEST=

Review URL: https://webrtc-codereview.appspot.com/507003

git-svn-id: http://webrtc.googlecode.com/svn/trunk@2082 4adac7df-926f-26a2-2b94-8c16560cd09d

src/modules/udp_transport/source/udp_transport_impl.h

@@ -25,6 +25,7 @@ public:
     // A factory that returns a wrapped UDP socket or equivalent.
     class SocketFactoryInterface {
     public:
+        virtual ~SocketFactoryInterface() {}
         virtual UdpSocketWrapper* CreateSocket(const WebRtc_Word32 id,
                                                UdpSocketManager* mgr,
                                                CallbackObj obj,