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

webrtc/modules/video_coding/utility/quality_scaler.h

 /*
  *  Copyright (c) 2014 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_UTILITY_QUALITY_SCALER_H_
 #define WEBRTC_MODULES_VIDEO_CODING_UTILITY_QUALITY_SCALER_H_
 
 #include <utility>
 
 #include "webrtc/common_types.h"
-#include "webrtc/video_encoder.h"
+#include "webrtc/api/video_codecs/video_encoder.h"
 #include "webrtc/base/optional.h"
 #include "webrtc/base/sequenced_task_checker.h"
 #include "webrtc/modules/video_coding/utility/moving_average.h"
 
 namespace webrtc {
 
 // An interface for signaling requests to limit or increase the resolution or
 // framerate of the captured video stream.
 class AdaptationObserverInterface {
  public:
@@ skipping 50 matching lines @@
   const int64_t sampling_period_ms_;
   bool fast_rampup_ GUARDED_BY(&task_checker_);
   MovingAverage average_qp_ GUARDED_BY(&task_checker_);
   MovingAverage framedrop_percent_ GUARDED_BY(&task_checker_);
 
   VideoEncoder::QpThresholds thresholds_ GUARDED_BY(&task_checker_);
 };
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_VIDEO_CODING_UTILITY_QUALITY_SCALER_H_