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

webrtc/video/video_receive_stream_unittest.cc

 /*
  *  Copyright 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.
  */
 
 #include <vector>
 
 #include "webrtc/test/gtest.h"
 #include "webrtc/test/gmock.h"
 
+#include "webrtc/api/video_codecs/video_decoder.h"
 #include "webrtc/base/criticalsection.h"
 #include "webrtc/base/event.h"
 #include "webrtc/media/base/fakevideorenderer.h"
 #include "webrtc/modules/pacing/packet_router.h"
 #include "webrtc/modules/rtp_rtcp/source/rtp_packet_to_send.h"
 #include "webrtc/modules/utility/include/process_thread.h"
 #include "webrtc/video/call_stats.h"
 #include "webrtc/video/video_receive_stream.h"
 #include "webrtc/system_wrappers/include/clock.h"
 #include "webrtc/system_wrappers/include/sleep.h"
 #include "webrtc/test/field_trial.h"
-#include "webrtc/video_decoder.h"
 
 using testing::_;
 using testing::Invoke;
 
 constexpr int kDefaultTimeOutMs = 50;
 
 namespace webrtc {
 
 namespace {
 
@@ skipping 93 matching lines @@
   video_receive_stream_->Start();
   EXPECT_CALL(mock_h264_video_decoder_, Decode(_, false, _, _, _));
   EXPECT_EQ(true,
             video_receive_stream_->OnRecoveredPacket(rtppacket.data(),
                                                      rtppacket.size()));
   EXPECT_CALL(mock_h264_video_decoder_, Release());
   // Make sure the decoder thread had a chance to run.
   init_decode_event_.Wait(kDefaultTimeOutMs);
 }
 }  // namespace webrtc