Make dummy device succeed at stopping recording/playout.

webrtc/modules/audio_device/dummy/audio_device_dummy.cc

Index: webrtc/modules/audio_device/dummy/audio_device_dummy.cc
diff --git a/webrtc/modules/audio_device/dummy/audio_device_dummy.cc b/webrtc/modules/audio_device/dummy/audio_device_dummy.cc
index 49619378695284965dc6e65356d0631eed2636c9..558bd1b4368412a42a54ca684eae7ccf55a4c164 100644
--- a/webrtc/modules/audio_device/dummy/audio_device_dummy.cc
+++ b/webrtc/modules/audio_device/dummy/audio_device_dummy.cc
@@ -69,13 +69,13 @@ bool AudioDeviceDummy::RecordingIsInitialized() const { return false; }
 
 int32_t AudioDeviceDummy::StartPlayout() { return -1; }
 
-int32_t AudioDeviceDummy::StopPlayout() { return -1; }
+int32_t AudioDeviceDummy::StopPlayout() { return 0; }
 
 bool AudioDeviceDummy::Playing() const { return false; }
 
 int32_t AudioDeviceDummy::StartRecording() { return -1; }
 
-int32_t AudioDeviceDummy::StopRecording() { return -1; }
+int32_t AudioDeviceDummy::StopRecording() { return 0; }
 
 bool AudioDeviceDummy::Recording() const { return false; }