Add a .gyp option to use dummy audio file devices.

webrtc/build/webrtc.gni

 # Copyright (c) 2014 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/config/arm.gni")
 import("//build/config/features.gni")
@@ skipping 94 matching lines @@
   # value that includes H.264, for example "Chrome". If FFmpeg is built without
   # H.264, compilation succeeds but |H264DecoderImpl| fails to initialize. See
   # also: |rtc_initialize_ffmpeg|.
   # CHECK THE OPENH264, FFMPEG AND H.264 LICENSES/PATENTS BEFORE BUILDING.
   # http://www.openh264.org, https://www.ffmpeg.org/
   rtc_use_h264 = proprietary_codecs && !is_android && !is_ios
 
   # Determines whether QUIC code will be built.
   rtc_use_quic = false
 
+  # By default, use normal platform audio support or dummy audio, but don't
+  # use file-based audio playout and record.
+  rtc_use_dummy_audio_file_devices = false
+
   # FFmpeg must be initialized for |H264DecoderImpl| to work. This can be done
   # by WebRTC during |H264DecoderImpl::InitDecode| or externally. FFmpeg must
   # only be initialized once. Projects that initialize FFmpeg externally, such
   # as Chromium, must turn this flag off so that WebRTC does not also
   # initialize.
   rtc_initialize_ffmpeg = !build_with_chromium
 
   # Build sources requiring GTK. NOTICE: This is not present in Chrome OS
   # build environments, even if available for Chromium builds.
   rtc_use_gtk = !build_with_chromium
 }
 
 # A second declare_args block, so that declarations within it can
 # depend on the possibly overridden variables in the first
 # declare_args block.
 declare_args() {
   # Include the iLBC audio codec?
   rtc_include_ilbc = !(build_with_chromium || build_with_mozilla)
 }
 
 # Make it possible to provide custom locations for some libraries (move these
 # up into declare_args should we need to actually use them for the GN build).
 rtc_libvpx_dir = "//third_party/libvpx"
 rtc_libyuv_dir = "//third_party/libyuv"
 rtc_opus_dir = "//third_party/opus"