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

webrtc/modules/video_coding/codecs/test/video_codec_test.h

 /*
  *  Copyright (c) 2017 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_MODULES_VIDEO_CODING_CODECS_TEST_VIDEO_CODEC_TEST_H_
 #define WEBRTC_MODULES_VIDEO_CODING_CODECS_TEST_VIDEO_CODEC_TEST_H_
 
 #include <memory>
 
+#include "webrtc/api/video_codecs/video_decoder.h"
+#include "webrtc/api/video_codecs/video_encoder.h"
 #include "webrtc/base/criticalsection.h"
 #include "webrtc/base/event.h"
 #include "webrtc/base/thread_annotations.h"
 #include "webrtc/test/gtest.h"
-#include "webrtc/video_decoder.h"
-#include "webrtc/video_encoder.h"
 
 namespace webrtc {
 
 class VideoCodecTest : public ::testing::Test {
  public:
   VideoCodecTest()
       : encode_complete_callback_(this),
         decode_complete_callback_(this),
         encoded_frame_event_(false /* manual reset */,
                              false /* initially signaled */),
@@ skipping 60 matching lines @@
 
   rtc::Event decoded_frame_event_;
   rtc::CriticalSection decoded_frame_section_;
   rtc::Optional<VideoFrame> decoded_frame_ GUARDED_BY(decoded_frame_section_);
   rtc::Optional<uint8_t> decoded_qp_ GUARDED_BY(decoded_frame_section_);
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_VIDEO_CODING_CODECS_TEST_VIDEO_CODEC_TEST_H_