Cleanup little things found when refactoring.

R=juberti@google.com

Review URL: https://webrtc-codereview.appspot.com/33519004

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@7880 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/base/sigslot.h b/base/sigslot.h
index 990d2ef..df26683 100644
--- a/base/sigslot.h
+++ b/base/sigslot.h
@@ -430,6 +430,7 @@
 	class _signal_base_interface
 	{
 	public:
+		virtual ~_signal_base_interface() {}
 		virtual void slot_disconnect(has_slots_interface* pslot) = 0;
 		virtual void slot_duplicate(const has_slots_interface* poldslot, has_slots_interface* pnewslot) = 0;
 	};