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

webrtc/modules/audio_device/dummy/file_audio_device_factory.cc

 /*
  *  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.
  */
 
 #include "webrtc/modules/audio_device/dummy/file_audio_device_factory.h"
 
 #include <cstdlib>
 #include <cstring>
 
+#include "webrtc/base/logging.h"
 #include "webrtc/modules/audio_device/dummy/file_audio_device.h"
 
 namespace webrtc {
 
 bool FileAudioDeviceFactory::_isConfigured = false;
 char FileAudioDeviceFactory::_inputAudioFilename[MAX_FILENAME_LEN] = "";
 char FileAudioDeviceFactory::_outputAudioFilename[MAX_FILENAME_LEN] = "";
 
 FileAudioDevice* FileAudioDeviceFactory::CreateFileAudioDevice(
     const int32_t id) {
   // Bail out here if the files haven't been set explicitly.
+  // audio_device_impl.cc should then fall back to dummy audio.
   if (!_isConfigured) {
-    printf("Was compiled with WEBRTC_DUMMY_AUDIO_PLAY_STATIC_FILE "
-           "but did not set input/output files to use. Bailing out.\n");
-    std::exit(1);
+    LOG(LS_WARNING) << "WebRTC configured with WEBRTC_DUMMY_FILE_DEVICES but "
+                    << "no device files supplied. Will fall back to dummy "
+                    << "audio.";
+
+    return nullptr;
   }
   return new FileAudioDevice(id, _inputAudioFilename, _outputAudioFilename);
 }
 
 void FileAudioDeviceFactory::SetFilenamesToUse(
     const char* inputAudioFilename, const char* outputAudioFilename) {
 #ifdef WEBRTC_DUMMY_FILE_DEVICES
   assert(strlen(inputAudioFilename) < MAX_FILENAME_LEN &&
          strlen(outputAudioFilename) < MAX_FILENAME_LEN);
 
   // Copy the strings since we don't know the lifetime of the input pointers.
   strncpy(_inputAudioFilename, inputAudioFilename, MAX_FILENAME_LEN);
   strncpy(_outputAudioFilename, outputAudioFilename, MAX_FILENAME_LEN);
   _isConfigured = true;
 #else
   // Sanity: must be compiled with the right define to run this.
   printf("Trying to use dummy file devices, but is not compiled "
          "with WEBRTC_DUMMY_FILE_DEVICES. Bailing out.\n");
   std::exit(1);
 #endif
 }
 
 }  // namespace webrtc