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

webrtc/test/fake_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_FAKE_ENCODER_H_
 #define WEBRTC_TEST_FAKE_ENCODER_H_
 
 #include <vector>
 #include <memory>
 
+#include "webrtc/api/video_codecs/video_encoder.h"
 #include "webrtc/base/criticalsection.h"
 #include "webrtc/base/sequenced_task_checker.h"
 #include "webrtc/base/task_queue.h"
 #include "webrtc/common_types.h"
 #include "webrtc/system_wrappers/include/clock.h"
-#include "webrtc/video_encoder.h"
 
 namespace webrtc {
 namespace test {
 
 class FakeEncoder : public VideoEncoder {
  public:
   explicit FakeEncoder(Clock* clock);
   virtual ~FakeEncoder() = default;
 
   // Sets max bitrate. Not thread-safe, call before registering the encoder.
@@ skipping 89 matching lines @@
   int current_queue_ ACCESS_ON(sequence_checker_);
   std::unique_ptr<rtc::TaskQueue> queue1_ ACCESS_ON(sequence_checker_);
   std::unique_ptr<rtc::TaskQueue> queue2_ ACCESS_ON(sequence_checker_);
   rtc::SequencedTaskChecker sequence_checker_;
 };
 
 }  // namespace test
 }  // namespace webrtc
 
 #endif  // WEBRTC_TEST_FAKE_ENCODER_H_