Support external audio mixer.

webrtc/media/engine/webrtcmediaengine_unittest.cc

Index: webrtc/media/engine/webrtcmediaengine_unittest.cc
diff --git a/webrtc/media/engine/webrtcmediaengine_unittest.cc b/webrtc/media/engine/webrtcmediaengine_unittest.cc
index 03e50a18c9a6dbaef712ea938647f398e7b4e963..77fbc87beb82cbccfa0cf82b6b27ebb7e54e4ff8 100644
--- a/webrtc/media/engine/webrtcmediaengine_unittest.cc
+++ b/webrtc/media/engine/webrtcmediaengine_unittest.cc
@@ -188,7 +188,8 @@ TEST(WebRtcMediaEngineFactoryTest, CreateOldApi) {
 
 TEST(WebRtcMediaEngineFactoryTest, CreateWithBuiltinDecoders) {
   std::unique_ptr<MediaEngineInterface> engine(WebRtcMediaEngineFactory::Create(
-      nullptr, webrtc::CreateBuiltinAudioDecoderFactory(), nullptr, nullptr));
+      nullptr, webrtc::CreateBuiltinAudioDecoderFactory(), nullptr, nullptr,
+      nullptr));
   EXPECT_TRUE(engine);
 }