Simplify passing video codec factories in media engine

webrtc/media/engine/nullwebrtcvideoengine.h

 /*
  *  Copyright (c) 2016 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 15 matching lines @@
 namespace cricket {
 
 class VideoMediaChannel;
 class WebRtcVideoDecoderFactory;
 class WebRtcVideoEncoderFactory;
 
 // Video engine implementation that does nothing and can be used in
 // CompositeMediaEngine.
 class NullWebRtcVideoEngine {
  public:
-  NullWebRtcVideoEngine() {}
-  ~NullWebRtcVideoEngine() {}
+  std::vector<VideoCodec> codecs() const { return std::vector<VideoCodec>(); }
 
-  void SetExternalDecoderFactory(WebRtcVideoDecoderFactory* decoder_factory) {}
-  void SetExternalEncoderFactory(WebRtcVideoEncoderFactory* encoder_factory) {}
-
-  void Init() {}
-
-  const std::vector<VideoCodec>& codecs() {
-    return codecs_;
-  }
-
-  RtpCapabilities GetCapabilities() {
-    RtpCapabilities capabilities;
-    return capabilities;
-  }
+  RtpCapabilities GetCapabilities() const { return RtpCapabilities(); }
 
   VideoMediaChannel* CreateChannel(webrtc::Call* call,
                                    const MediaConfig& config,
                                    const VideoOptions& options) {
     return nullptr;
   }
-
- private:
-  std::vector<VideoCodec> codecs_;
 };
 
 }  // namespace cricket
 
 #endif  // WEBRTC_MEDIA_ENGINE_NULLWEBRTCVIDEOENGINE_H_