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

webrtc/video/payload_router.h

 /*
  *  Copyright (c) 2015 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_VIDEO_PAYLOAD_ROUTER_H_
 #define WEBRTC_VIDEO_PAYLOAD_ROUTER_H_
 
 #include <vector>
 
+#include "webrtc/api/video_codecs/video_encoder.h"
 #include "webrtc/base/constructormagic.h"
 #include "webrtc/base/criticalsection.h"
 #include "webrtc/base/thread_annotations.h"
 #include "webrtc/common_types.h"
 #include "webrtc/config.h"
-#include "webrtc/video_encoder.h"
 #include "webrtc/system_wrappers/include/atomic32.h"
 
 namespace webrtc {
 
 class RTPFragmentationHeader;
 class RtpRtcp;
 struct RTPVideoHeader;
 
 // PayloadRouter routes outgoing data to the correct sending RTP module, based
 // on the simulcast layer in RTPVideoHeader.
@@ skipping 27 matching lines @@
   // Rtp modules are assumed to be sorted in simulcast index order. Not owned.
   const std::vector<RtpRtcp*> rtp_modules_;
   const int payload_type_;
 
   RTC_DISALLOW_COPY_AND_ASSIGN(PayloadRouter);
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_VIDEO_PAYLOAD_ROUTER_H_