Move video_encoder.h and video_decoder.h to /api and create GN targets for them

webrtc/media/engine/videoencodersoftwarefallbackwrapper.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.
  */
 
 #ifndef WEBRTC_MEDIA_ENGINE_VIDEOENCODERSOFTWAREFALLBACKWRAPPER_H_
 #define WEBRTC_MEDIA_ENGINE_VIDEOENCODERSOFTWAREFALLBACKWRAPPER_H_
 
 #include <memory>
 #include <string>
 #include <vector>
 
+#include "webrtc/api/video_codecs/video_encoder.h"
 #include "webrtc/media/base/codec.h"
-#include "webrtc/video_encoder.h"
 
 namespace webrtc {
 
 // Class used to wrap external VideoEncoders to provide a fallback option on
 // software encoding when a hardware encoder fails to encode a stream due to
 // hardware restrictions, such as max resolution.
 class VideoEncoderSoftwareFallbackWrapper : public VideoEncoder {
  public:
   VideoEncoderSoftwareFallbackWrapper(const cricket::VideoCodec& codec,
                                       webrtc::VideoEncoder* encoder);
@@ skipping 39 matching lines @@
   webrtc::VideoEncoder* const encoder_;
 
   std::unique_ptr<webrtc::VideoEncoder> fallback_encoder_;
   std::string fallback_implementation_name_;
   EncodedImageCallback* callback_;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MEDIA_ENGINE_VIDEOENCODERSOFTWAREFALLBACKWRAPPER_H_