Fix all -Wnon-virtual-dtor warnings.

webrtc/api/peerconnectionfactory_unittest.cc

 /*
  *  Copyright 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 46 matching lines @@
 static const char kStunIceServerWithIPv4Address[] = "stun:1.2.3.4:1234";
 static const char kStunIceServerWithIPv4AddressWithoutPort[] = "stun:1.2.3.4";
 static const char kStunIceServerWithIPv6Address[] = "stun:[2401:fa00:4::]:1234";
 static const char kStunIceServerWithIPv6AddressWithoutPort[] =
     "stun:[2401:fa00:4::]";
 static const char kTurnIceServerWithIPv6Address[] =
     "turn:test@[2401:fa00:4::]:1234";
 
 class NullPeerConnectionObserver : public PeerConnectionObserver {
  public:
+  virtual ~NullPeerConnectionObserver() = default;
   virtual void OnMessage(const std::string& msg) {}
   virtual void OnSignalingMessage(const std::string& msg) {}
   virtual void OnSignalingChange(
       PeerConnectionInterface::SignalingState new_state) {}
   virtual void OnAddStream(MediaStreamInterface* stream) {}
   virtual void OnRemoveStream(MediaStreamInterface* stream) {}
   virtual void OnDataChannel(DataChannelInterface* data_channel) {}
   virtual void OnRenegotiationNeeded() {}
   virtual void OnIceConnectionChange(
       PeerConnectionInterface::IceConnectionState new_state) {}
@@ skipping 270 matching lines @@
   track->set_enabled(false);
   EXPECT_TRUE(capturer->CaptureFrame());
   EXPECT_EQ(2, local_renderer.num_rendered_frames());
   EXPECT_TRUE(local_renderer.black_frame());
 
   track->set_enabled(true);
   EXPECT_TRUE(capturer->CaptureFrame());
   EXPECT_EQ(3, local_renderer.num_rendered_frames());
   EXPECT_FALSE(local_renderer.black_frame());
 }