mustash: Convert TraySupervisedUserTest to AshTest

ash/common/test/ash_test.cc

Index: ash/common/test/ash_test.cc
diff --git a/ash/common/test/ash_test.cc b/ash/common/test/ash_test.cc
index 32744b9c82da250a983050b173c90ad0847995bc..7a1c905d0492a1ad666007052c2b830e78b3c24a 100644
--- a/ash/common/test/ash_test.cc
+++ b/ash/common/test/ash_test.cc
@@ -8,6 +8,7 @@
 #include "ash/common/system/status_area_widget.h"
 #include "ash/common/test/ash_test_impl.h"
 #include "ash/common/test/test_session_state_delegate.h"
+#include "ash/common/test/test_system_tray_delegate.h"
 #include "ash/common/wm_root_window_controller.h"
 #include "ash/common/wm_shell.h"
 #include "ash/common/wm_window.h"
@@ -40,6 +41,12 @@ SystemTray* AshTest::GetPrimarySystemTray() {
   return GetPrimaryShelf()->GetStatusAreaWidget()->system_tray();
 }
 
+// static
+test::TestSystemTrayDelegate* AshTest::GetSystemTrayDelegate() {
+  return static_cast<test::TestSystemTrayDelegate*>(
+      WmShell::Get()->system_tray_delegate());
+}
+
 bool AshTest::SupportsMultipleDisplays() const {
   return test_impl_->SupportsMultipleDisplays();
 }