Fix audio related GN args handling for Chrome OS

media/media_options.gni

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/chromecast_build.gni")
 import("//build/config/features.gni")
 import("//build/config/headless_build.gni")
 
 declare_args() {
   # Allows distributions to link pulseaudio directly (DT_NEEDED) instead of
@@ skipping 12 matching lines @@
 
   # iOS doesn't use ffmpeg, libvpx.
   if (is_ios) {
     media_use_ffmpeg = false
     media_use_libvpx = false
   }
 
   # Override to dynamically link the cras (ChromeOS audio) library.
   use_cras = false
 
-  # Enables runtime selection of PulseAudio library.
-  use_pulseaudio = false
-
-  # Enables runtime selection of ALSA library for audio.
-  use_alsa = false
-
-  # Alsa should be used on non-Android, non-Mac POSIX systems, and Chromecast
-  # builds for desktop Linux.
-  if (is_posix && !is_headless && !is_android && !is_mac &&
-      (!is_chromecast || is_cast_desktop_build)) {
-    use_alsa = true
-    if (!use_cras) {
-      use_pulseaudio = true
-    }
-  }
-
   # Use low-memory buffers on non-Android builds of Chromecast.
   use_low_memory_buffer = is_chromecast && !is_android
 
   # Enables AC3/EAC3 audio demuxing. This is enabled only on Chromecast, since
   # it only provides demuxing, and is only useful for AC3/EAC3 audio
   # pass-through to HDMI sink on Chromecast.
   enable_ac3_eac3_audio_demuxing = proprietary_codecs && is_chromecast
 
   enable_mse_mpeg2ts_stream_parser = proprietary_codecs && is_chromecast
 
   # Enable HEVC/H265 demuxing. Actual decoding must be provided by the
   # platform. Enable by default for Chromecast.
   enable_hevc_demuxing = proprietary_codecs && is_chromecast
 
   # Experiment to enable mojo media application: http://crbug.com/431776
   # Valid options are:
   # - "none": Do not use mojo media application.
   # - "browser": Use mojo media application hosted in the browser process.
   # - "gpu": Use mojo media application hosted in the gpu process.
   # - "utility": Use mojo media application hosted in the utility process.
   enable_mojo_media = "none"
 
   # TODO(GYP): This should be a platform define.
   is_openbsd = false
 }
+
+declare_args() {
+  # Enables runtime selection of PulseAudio library.
+  use_pulseaudio = false
+
+  # Enables runtime selection of ALSA library for audio.
+  use_alsa = false
+
+  # Alsa should be used on non-Android, non-Mac POSIX systems, and Chromecast
+  # builds for desktop Linux.
+  if (is_posix && !is_headless && !is_android && !is_mac &&
+      (!is_chromecast || is_cast_desktop_build)) {
+    use_alsa = true
+    if (!use_cras) {
+      use_pulseaudio = true
+    }
+  }
+}