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

webrtc/test/configurable_frame_size_encoder.h

 /*
  *  Copyright (c) 2013 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_TEST_CONFIGURABLE_FRAME_SIZE_ENCODER_H_
 #define WEBRTC_TEST_CONFIGURABLE_FRAME_SIZE_ENCODER_H_
 
 #include <memory>
 #include <vector>
 
-#include "webrtc/video_encoder.h"
+#include "webrtc/api/video_codecs/video_encoder.h"
 
 namespace webrtc {
 namespace test {
 
 class ConfigurableFrameSizeEncoder : public VideoEncoder {
  public:
   explicit ConfigurableFrameSizeEncoder(size_t max_frame_size);
   virtual ~ConfigurableFrameSizeEncoder();
 
   int32_t InitEncode(const VideoCodec* codec_settings,
@@ skipping 22 matching lines @@
   EncodedImageCallback* callback_;
   const size_t max_frame_size_;
   size_t current_frame_size_;
   std::unique_ptr<uint8_t[]> buffer_;
 };
 
 }  // namespace test
 }  // namespace webrtc
 
 #endif  // WEBRTC_TEST_CONFIGURABLE_FRAME_SIZE_ENCODER_H_