Convert //ash from scoped_ptr to std::unique_ptr

ash/system/chromeos/audio/tray_audio_chromeos.cc

Index: ash/system/chromeos/audio/tray_audio_chromeos.cc
diff --git a/ash/system/chromeos/audio/tray_audio_chromeos.cc b/ash/system/chromeos/audio/tray_audio_chromeos.cc
index 3d420ff6e655efc91d6ca93beb48897909439fb8..1a99133cba8ecbc4a0e5cefd02796073422e97c1 100644
--- a/ash/system/chromeos/audio/tray_audio_chromeos.cc
+++ b/ash/system/chromeos/audio/tray_audio_chromeos.cc
@@ -18,8 +18,9 @@ using system::TrayAudioDelegate;
 using system::TrayAudioDelegateChromeOs;
 
 TrayAudioChromeOs::TrayAudioChromeOs(SystemTray* system_tray)
-    : TrayAudio(system_tray,
-                scoped_ptr<TrayAudioDelegate>(new TrayAudioDelegateChromeOs())),
+    : TrayAudio(
+          system_tray,
+          std::unique_ptr<TrayAudioDelegate>(new TrayAudioDelegateChromeOs())),
       audio_detail_view_(NULL) {
   chromeos::DBusThreadManager::Get()->GetPowerManagerClient()->AddObserver(
       this);