Fix all -Wnon-virtual-dtor warnings.

webrtc/media/engine/webrtcvideoengine2.h

 /*
  *  Copyright (c) 2014 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 56 matching lines @@
 std::vector<VideoCodec> DefaultVideoCodecList();
 
 class UnsignalledSsrcHandler {
  public:
   enum Action {
     kDropPacket,
     kDeliverPacket,
   };
   virtual Action OnUnsignalledSsrc(WebRtcVideoChannel2* channel,
                                    uint32_t ssrc) = 0;
+  virtual ~UnsignalledSsrcHandler() = default;
 };
 
 // TODO(pbos): Remove, use external handlers only.
 class DefaultUnsignalledSsrcHandler : public UnsignalledSsrcHandler {
  public:
   DefaultUnsignalledSsrcHandler();
   Action OnUnsignalledSsrc(WebRtcVideoChannel2* channel,
                            uint32_t ssrc) override;
 
   rtc::VideoSinkInterface<VideoFrame>* GetDefaultSink() const;
   void SetDefaultSink(VideoMediaChannel* channel,
                       rtc::VideoSinkInterface<VideoFrame>* sink);
+  virtual ~DefaultUnsignalledSsrcHandler() = default;
 
  private:
   uint32_t default_recv_ssrc_;
   rtc::VideoSinkInterface<VideoFrame>* default_sink_;
 };
 
 // WebRtcVideoEngine2 is used for the new native WebRTC Video API (webrtc:1667).
 class WebRtcVideoEngine2 {
  public:
   WebRtcVideoEngine2();
-  ~WebRtcVideoEngine2();
+  virtual ~WebRtcVideoEngine2();
 
   // Basic video engine implementation.
   void Init();
 
   WebRtcVideoChannel2* CreateChannel(webrtc::Call* call,
                                      const MediaConfig& config,
                                      const VideoOptions& options);
 
   const std::vector<VideoCodec>& codecs() const;
   RtpCapabilities GetCapabilities() const;
@@ skipping 424 matching lines @@
   // TODO(deadbeef): Don't duplicate information between
   // send_params/recv_params, rtp_extensions, options, etc.
   VideoSendParameters send_params_;
   VideoOptions default_send_options_;
   VideoRecvParameters recv_params_;
 };
 
 }  // namespace cricket
 
 #endif  // WEBRTC_MEDIA_ENGINE_WEBRTCVIDEOENGINE2_H_