chromeos: convert remaining AshTest usage to AshTestBase

ash/system/audio/tray_audio_unittest.cc

Index: ash/system/audio/tray_audio_unittest.cc
diff --git a/ash/system/audio/tray_audio_unittest.cc b/ash/system/audio/tray_audio_unittest.cc
index 16d7e8942c20a33e71bb8883613958068b2a7f77..592f7550d7ffdd956f4b05fe8df5f0c0d6749ae1 100644
--- a/ash/system/audio/tray_audio_unittest.cc
+++ b/ash/system/audio/tray_audio_unittest.cc
@@ -5,11 +5,11 @@
 #include "ash/system/audio/tray_audio.h"
 
 #include "ash/system/tray/system_tray.h"
-#include "ash/test/ash_test.h"
+#include "ash/test/ash_test_base.h"
 
 namespace ash {
 
-using TrayAudioTest = AshTest;
+using TrayAudioTest = test::AshTestBase;
 
 // Tests that the volume popup view can be explicitly shown.
 TEST_F(TrayAudioTest, ShowPopUpVolumeView) {