Fix all -Wnon-virtual-dtor warnings.

webrtc/p2p/base/turnserver.h

Index: webrtc/p2p/base/turnserver.h
diff --git a/webrtc/p2p/base/turnserver.h b/webrtc/p2p/base/turnserver.h
index c9eb803d65c949c93617cdcbf6f28e810b3ed40a..2bc3650f0916f6f63ad677b3de6f2fd8fd14d7f6 100644
--- a/webrtc/p2p/base/turnserver.h
+++ b/webrtc/p2p/base/turnserver.h
@@ -144,6 +144,7 @@ class TurnAuthInterface {
   // Return true if the given username and realm are valid, or false if not.
   virtual bool GetKey(const std::string& username, const std::string& realm,
                       std::string* key) = 0;
+  virtual ~TurnAuthInterface() = default;
 };
 
 // An interface enables Turn Server to control redirection behavior.