Add an ALSA output to the motown audio server.

services/media/audio/BUILD.gn

 # Copyright 2015 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("//mojo/public/mojo_application.gni")
 import("//mojo/public/tools/bindings/mojom.gni")
 
 group("audio") {
   deps = [
     ":audio_server",
@@ skipping 17 matching lines @@
     "audio_server_app.cc",
     "audio_server_impl.cc",
     "audio_track_impl.cc",
     "audio_track_to_output_link.cc",
     "platform/generic/mix_kernels.cc",
     "platform/generic/standard_output_base.cc",
     "platform/generic/throttle_output.cc",
   ]
 
   libs = []
+
+  if (is_linux) {
+    sources += [ "platform/linux/alsa_output.cc" ]
+    libs += [ "asound" ]
+  }
 }