Build WebRTC with data channel only.

webrtc/pc/nullaudiofactory.cc

Index: webrtc/pc/nullaudiofactory.cc
diff --git a/webrtc/pc/nullaudiofactory.cc b/webrtc/pc/nullaudiofactory.cc
new file mode 100644
index 0000000000000000000000000000000000000000..6d62fb203f3201df2a2cf693279465538742e899
--- /dev/null
+++ b/webrtc/pc/nullaudiofactory.cc
@@ -0,0 +1,44 @@
+/*
+ *  Copyright 2017 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.
+ */
+
+// Adding 'nogncheck' to disable the gn include headers check.
+// We don't want the null implementation to depend on the audio related targets.
+#include "webrtc/api/audio/audio_mixer.h"  // nogncheck
+#include "webrtc/api/peerconnectioninterface.h"
+#include "webrtc/base/scoped_ref_ptr.h"
+#include "webrtc/base/thread.h"
+
+namespace cricket {
+class WebRtcVideoEncoderFactory;
+class WebRtcVideoDecoderFactory;
+}  // namespace cricket
+
+namespace webrtc {
+
+rtc::scoped_refptr<PeerConnectionFactoryInterface>
+CreatePeerConnectionFactory() {
+  return CreatePeerConnectionFactory(nullptr, nullptr);
+}
+
+rtc::scoped_refptr<PeerConnectionFactoryInterface>
+CreatePeerConnectionFactoryWithAudioMixer(
+    rtc::Thread* network_thread,
+    rtc::Thread* worker_thread,
+    rtc::Thread* signaling_thread,
+    AudioDeviceModule* default_adm,
+    cricket::WebRtcVideoEncoderFactory* encoder_factory,
+    cricket::WebRtcVideoDecoderFactory* decoder_factory,
+    rtc::scoped_refptr<AudioMixer> audio_mixer) {
+  return CreatePeerConnectionFactoryWithAudioMixer(
+      network_thread, worker_thread, signaling_thread, default_adm, nullptr,
+      nullptr, encoder_factory, decoder_factory, audio_mixer);
+}
+
+}  // namespace webrtc