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

webrtc/modules/video_coding/BUILD.gn

 # 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.
 
 import("../../webrtc.gni")
 
@@ skipping 111 matching lines @@
     "utility/vp8_header_parser.h",
   ]
 
   if (!build_with_chromium && is_clang) {
     # Suppress warnings from the Chromium Clang plugin (bugs.webrtc.org/163).
     suppressed_configs += [ "//build/config/clang:find_bad_constructs" ]
   }
 
   deps = [
     "../..:webrtc_common",
+    "../../api:video_decoder_api",
+    "../../api:video_encoder_api",
     "../../base:rtc_base_approved",
     "../../base:rtc_numerics",
     "../../base:rtc_task_queue",
     "../../common_video",
     "../../modules/rtp_rtcp:rtp_rtcp",
     "../../system_wrappers",
   ]
 }
 
 rtc_static_library("webrtc_h264") {
@@ skipping 75 matching lines @@
   configs += [ "//build/config/compiler:no_size_t_to_int_warning" ]
 
   if (!build_with_chromium && is_clang) {
     # Suppress warnings from the Chromium Clang plugin (bugs.webrtc.org/163).
     suppressed_configs += [ "//build/config/clang:find_bad_constructs" ]
   }
 
   deps = [
     ":video_coding_utility",
     "../..:webrtc_common",
+    "../../api:video_encoder_api",
     "../../base:rtc_base_approved",
     "../../common_video",
     "../../system_wrappers",
   ]
   if (rtc_build_libvpx) {
     deps += [ rtc_libvpx_dir ]
   }
 }
 
 rtc_static_library("webrtc_vp9") {
@@ skipping 78 matching lines @@
     if (!build_with_chromium && is_clang) {
       # Suppress warnings from the Chromium Clang plugin (bugs.webrtc.org/163).
       suppressed_configs += [ "//build/config/clang:find_bad_constructs" ]
     }
 
     deps = [
       ":video_coding",
       ":video_coding_utility",
       ":webrtc_vp8",
       "../..:webrtc_common",
+      "../../api:video_encoder_api",
+      "../../api:video_decoder_api",
       "../../base:rtc_base_approved",
       "../../common_video:common_video",
       "../../system_wrappers:system_wrappers",
       "../../test:test_support",
       "../../test:video_test_common",
       "../../test:video_test_support",
     ]
   }
 
   rtc_source_set("video_coding_videoprocessor_integration_test") {
@@ skipping 185 matching lines @@
       sources += [ "codecs/h264/h264_encoder_impl_unittest.cc" ]
     }
     deps = [
       ":video_codecs_test_framework",
       ":video_coding",
       ":video_coding_utility",
       ":webrtc_h264",
       ":webrtc_vp8",
       ":webrtc_vp9",
       "../..:webrtc_common",
+      "../../api:video_encoder_api",
       "../../api:video_frame_api",
       "../../base:rtc_base",
       "../../base:rtc_base_approved",
       "../../base:rtc_task_queue",
       "../../common_video:common_video",
       "../../system_wrappers:metrics_default",
       "../../system_wrappers:system_wrappers",
       "../../test:field_trial",
       "../../test:test_support",
       "../../test:video_test_common",
@@ skipping 12 matching lines @@
     }
 
     # TODO(jschuh): bugs.webrtc.org/1348: fix this warning.
     configs += [ "//build/config/compiler:no_size_t_to_int_warning" ]
     if (!build_with_chromium && is_clang) {
       # Suppress warnings from the Chromium Clang plugin (bugs.webrtc.org/163).
       suppressed_configs += [ "//build/config/clang:find_bad_constructs" ]
     }
   }
 }