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

webrtc/media/BUILD.gn

 # Copyright (c) 2016 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("//build/config/linux/pkg_config.gni")
 import("../webrtc.gni")
@@ skipping 208 matching lines @@
     deps += [ "../modules/video_capture:video_capture_internal_impl" ]
   }
   deps += [
     ":rtc_media_base",
     "..:webrtc_common",
     "../api:call_api",
     "../api:transport_api",
     "../api:video_frame_api",
     "../api/audio_codecs:audio_codecs_api",
     "../api/audio_codecs:builtin_audio_decoder_factory",
+    "../api/video_codecs:video_codecs_api",
     "../base:rtc_base",
     "../base:rtc_base_approved",
     "../call",
     "../common_video:common_video",
     "../modules/audio_coding:rent_a_codec",
     "../modules/audio_device:audio_device",
     "../modules/audio_mixer:audio_mixer_impl",
     "../modules/audio_processing:audio_processing",
     "../modules/video_capture:video_capture_module",
     "../modules/video_coding",
@@ skipping 59 matching lines @@
       # Suppress warnings from the Chromium Clang plugin (bugs.webrtc.org/163).
       suppressed_configs += [ "//build/config/clang:find_bad_constructs" ]
     }
 
     deps += [
       ":rtc_media",
       ":rtc_media_base",
       "..:webrtc_common",
       "../api:call_api",
       "../api:video_frame_api",
+      "../api/video_codecs:video_codecs_api",
       "../base:rtc_base",
       "../base:rtc_base_approved",
       "../base:rtc_base_tests_main",
       "../base:rtc_base_tests_utils",
       "../call:call_interfaces",
       "../test:test_support",
       "//testing/gtest",
     ]
     public_deps += [ "//testing/gmock" ]
   }
@@ skipping 113 matching lines @@
     if (is_ios) {
       deps += [ ":rtc_media_unittests_bundle_data" ]
     }
 
     deps += [
       ":rtc_media",
       ":rtc_media_base",
       ":rtc_unittest_main",
       "../api:video_frame_api",
       "../api/audio_codecs:builtin_audio_decoder_factory",
+      "../api/video_codecs:video_codecs_api",
       "../audio",
       "../base:rtc_base",
       "../base:rtc_base_approved",
       "../base:rtc_base_tests_utils",
       "../call:call_interfaces",
       "../common_video:common_video",
       "../logging:rtc_event_log_api",
       "../modules/audio_device:mock_audio_device",
       "../modules/audio_processing:audio_processing",
       "../modules/video_coding:video_coding_utility",
       "../modules/video_coding:webrtc_vp8",
       "../p2p:rtc_p2p_unittests",
       "../system_wrappers:metrics_default",
       "../test:test_support",
       "../voice_engine:voice_engine",
     ]
   }
 }