[Chromecast] Fix bug when audio device ID is empty string.

chromecast/media/service/cast_renderer.cc

Index: chromecast/media/service/cast_renderer.cc
diff --git a/chromecast/media/service/cast_renderer.cc b/chromecast/media/service/cast_renderer.cc
index 4cd246ca4c77be4bb4b9247301d3c84b72069fcb..e1c9fbe3c2b66ffdcbaf304229a506213e190052 100644
--- a/chromecast/media/service/cast_renderer.cc
+++ b/chromecast/media/service/cast_renderer.cc
@@ -62,7 +62,9 @@ CastRenderer::CastRenderer(
     MediaResourceTracker* media_resource_tracker)
     : backend_factory_(backend_factory),
       task_runner_(task_runner),
-      audio_device_id_(audio_device_id),
+      audio_device_id_(audio_device_id.empty()
+                           ? ::media::AudioDeviceDescription::kDefaultDeviceId
+                           : audio_device_id),
       video_mode_switcher_(video_mode_switcher),
       video_resolution_policy_(video_resolution_policy),
       media_resource_tracker_(media_resource_tracker),
@@ -102,12 +104,9 @@ void CastRenderer::Initialize(::media::MediaResource* media_resource,
       (load_type == kLoadTypeMediaStream)
           ? MediaPipelineDeviceParams::kModeIgnorePts
           : MediaPipelineDeviceParams::kModeSyncPts;
-  std::string device_id = audio_device_id_;
-  if (device_id == "")
-    device_id = ::media::AudioDeviceDescription::kDefaultDeviceId;
 
   AudioContentType content_type;
-  if (device_id == kAlarmAudioDeviceId) {
+  if (audio_device_id_ == kAlarmAudioDeviceId) {
     content_type = AudioContentType::kAlarm;
   } else if (audio_device_id_ == kTtsAudioDeviceId) {
     content_type = AudioContentType::kCommunication;