[Chromecast] Implement new volume control API

chromecast/media/cma/backend/alsa/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("//build/buildflag_header.gni")
 import("//build/config/chromecast_build.gni")
 import("//chromecast/chromecast.gni")
 import("//media/media_options.gni")
 import("//testing/test.gni")
 
@@ skipping 32 matching lines @@
     "media_pipeline_backend_alsa.cc",
     "media_pipeline_backend_alsa.h",
     "stream_mixer_alsa.cc",
     "stream_mixer_alsa.h",
     "stream_mixer_alsa_input.cc",
     "stream_mixer_alsa_input.h",
     "stream_mixer_alsa_input_impl.cc",
     "stream_mixer_alsa_input_impl.h",
   ]
 
+  if (enable_assistant) {
+    sources += [ "volume_control.cc" ]
+  }
+
   libs = [ "asound" ]
 
   deps = [
     ":alsa_features",
     ":audio_filter_includes",
     ":slew_volume",
     "//base",
     "//chromecast/base",
     "//chromecast/media/base",
     "//chromecast/media/cma/backend:null",
@@ skipping 78 matching lines @@
   public_deps = [
     ":alsa_cma_backend",
   ]
 
   deps = [
     "//base",
     "//media",
     "//testing/gmock",
   ]
 }