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

PRESUBMIT.py

 # Copyright (c) 2012 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 json
 import os
 import re
 import subprocess
 import sys
 
 
 # Files and directories that are *skipped* by cpplint in the presubmit script.
 CPPLINT_BLACKLIST = [
   'tools-webrtc',
+  'webrtc/api/video_codecs/video_decoder.h',
+  'webrtc/api/video_codecs/video_encoder.h',
   'webrtc/base',
   'webrtc/examples/objc',
   'webrtc/media',
   'webrtc/modules/audio_coding',
   'webrtc/modules/audio_conference_mixer',
   'webrtc/modules/audio_device',
   'webrtc/modules/audio_processing',
   'webrtc/modules/desktop_capture',
   'webrtc/modules/include/module_common_types.h',
   'webrtc/modules/media_file',
   'webrtc/modules/utility',
   'webrtc/modules/video_capture',
   'webrtc/p2p',
   'webrtc/pc',
   'webrtc/sdk/android/src/jni',
   'webrtc/sdk/objc',
   'webrtc/system_wrappers',
   'webrtc/test',
   'webrtc/voice_engine',
   'webrtc/call.h',
   'webrtc/common_types.h',
   'webrtc/common_types.cc',
-  'webrtc/video_decoder.h',
-  'webrtc/video_encoder.h',
   'webrtc/video_send_stream.h',
 ]
 
 # These filters will always be removed, even if the caller specifies a filter
 # set, as they are problematic or broken in some way.
 #
 # Justifications for each filter:
 # - build/c++11         : Rvalue ref checks are unreliable (false positives),
 #                         include file and feature blacklists are
 #                         google3-specific.
@@ skipping 522 matching lines @@
       input_api, output_api))
   results.extend(input_api.canned_checks.CheckChangeHasDescription(
       input_api, output_api))
   results.extend(_CheckChangeHasBugField(input_api, output_api))
   results.extend(input_api.canned_checks.CheckChangeHasTestField(
       input_api, output_api))
   results.extend(input_api.canned_checks.CheckTreeIsOpen(
       input_api, output_api,
       json_url='http://webrtc-status.appspot.com/current?format=json'))
   return results