Added an empty AudioTransportProxy to AudioState.

webrtc/call/call_unittest.cc

Index: webrtc/call/call_unittest.cc
diff --git a/webrtc/call/call_unittest.cc b/webrtc/call/call_unittest.cc
index 1cdd48ad964a3d79653dc44f94f5481cd217b250..057be9c46b442d4415f25832f41e10c565de33d5 100644
--- a/webrtc/call/call_unittest.cc
+++ b/webrtc/call/call_unittest.cc
@@ -15,6 +15,7 @@
 #include "webrtc/call.h"
 #include "webrtc/logging/rtc_event_log/rtc_event_log.h"
 #include "webrtc/modules/audio_coding/codecs/mock/mock_audio_decoder_factory.h"
+#include "webrtc/modules/audio_device/include/mock_audio_device.h"
 #include "webrtc/test/gtest.h"
 #include "webrtc/test/mock_voice_engine.h"
 
@@ -26,6 +27,8 @@ struct CallHelper {
       : voice_engine_(decoder_factory) {
     webrtc::AudioState::Config audio_state_config;
     audio_state_config.voice_engine = &voice_engine_;
+    ON_CALL(voice_engine_, audio_device_module())
+        .WillByDefault(Return(&mock_audio_device_));
     webrtc::Call::Config config(&event_log_);
     config.audio_state = webrtc::AudioState::Create(audio_state_config);
     call_.reset(webrtc::Call::Create(config));
@@ -35,6 +38,7 @@ struct CallHelper {
 
  private:
   testing::NiceMock<webrtc::test::MockVoiceEngine> voice_engine_;
+  testing::NiceMock<webrtc::test::MockAudioDeviceModule> mock_audio_device_;
   webrtc::RtcEventLogNullImpl event_log_;
   std::unique_ptr<webrtc::Call> call_;
 };