Add code for dummy file audio to fallback to dummy audio.

webrtc/modules/audio_device/audio_device_impl.cc

Index: webrtc/modules/audio_device/audio_device_impl.cc
diff --git a/webrtc/modules/audio_device/audio_device_impl.cc b/webrtc/modules/audio_device/audio_device_impl.cc
index bfcbb00e48a492bdcffa20b9870411ba3d04ad56..d8dce9e88c7295f5ae952e2762bd5ee1d42df8e8 100644
--- a/webrtc/modules/audio_device/audio_device_impl.cc
+++ b/webrtc/modules/audio_device/audio_device_impl.cc
@@ -186,7 +186,13 @@ int32_t AudioDeviceModuleImpl::CreatePlatformSpecificObjects() {
   LOG(INFO) << "Dummy Audio APIs will be utilized";
 #elif defined(WEBRTC_DUMMY_FILE_DEVICES)
   ptrAudioDevice = FileAudioDeviceFactory::CreateFileAudioDevice(Id());
-  LOG(INFO) << "Will use file-playing dummy device.";
+  if (ptrAudioDevice) {
+    LOG(INFO) << "Will use file-playing dummy device.";
+  } else {
+    // Create a dummy device instead.
+    ptrAudioDevice = new AudioDeviceDummy(Id());
+    LOG(INFO) << "Dummy Audio APIs will be utilized";
+  }
 #else
   AudioLayer audioLayer(PlatformAudioLayer());