Refactor webrtc/modules/audio_conference_mixer for GN check

.gn

 # Copyright (c) 2015 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/dotfile_settings.gni")
 
 # The location of the build configuration file.
 buildconfig = "//build/config/BUILDCONFIG.gn"
 
 # The secondary source root is a parallel directory tree where
 # GN build files are placed when they can not be placed directly
 # in the source tree, e.g. for third party source trees.
 secondary_source = "//build/secondary/"
 
 # These are the targets to check headers for by default. The files in targets
 # matching these patterns (see "gn help label_pattern" for format) will have
 # their includes checked for proper dependencies when you run either
 # "gn check" or "gn gen --check".
 # TODO(kjellander): Keep adding paths to this list as work in webrtc:5589 is done.
 check_targets = [
   "//webrtc/api/*",
   "//webrtc/audio/*",
   "//webrtc/modules/audio_coding/*",
+  "//webrtc/modules/audio_conference_mixer/*",
   "//webrtc/modules/audio_device/*",
   "//webrtc/modules/audio_mixer/*",
   "//webrtc/modules/audio_processing/*",
   "//webrtc/modules/media_file/*",
   "//webrtc/modules/pacing/*",
   "//webrtc/modules/video_capture/*",
   "//webrtc/modules/video_coding/*",
   "//webrtc/stats:rtc_stats",
   "//webrtc/voice_engine",
   "//webrtc/voice_engine:level_indicator",
 ]
 
 # These are the list of GN files that run exec_script. This whitelist exists
 # to force additional review for new uses of exec_script, which is strongly
 # discouraged except for gypi_to_gn calls.
 exec_script_whitelist = build_dotfile_settings.exec_script_whitelist + [
                           "//third_party/boringssl/BUILD.gn",
                           "//third_party/openh264/BUILD.gn",
                           "//third_party/opus/BUILD.gn",
                           "//webrtc/modules/video_render/BUILD.gn",
                         ]