mash: Port TrayUpdateTest to AshTest

ash/common/test/wm_shell_test_api.cc

Index: ash/common/test/wm_shell_test_api.cc
diff --git a/ash/common/test/wm_shell_test_api.cc b/ash/common/test/wm_shell_test_api.cc
new file mode 100644
index 0000000000000000000000000000000000000000..39305eaf885b3a2a08b839fb8c795b02124b8044
--- /dev/null
+++ b/ash/common/test/wm_shell_test_api.cc
@@ -0,0 +1,21 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ash/common/test/wm_shell_test_api.h"
+
+#include "ash/common/system/tray/system_tray_delegate.h"
+#include "ash/common/wm_shell.h"
+
+namespace ash {
+
+WmShellTestApi::WmShellTestApi() {}
+
+WmShellTestApi::~WmShellTestApi() {}
+
+void WmShellTestApi::SetSystemTrayDelegate(
+    std::unique_ptr<SystemTrayDelegate> delegate) {
+  WmShell::Get()->SetSystemTrayDelegate(std::move(delegate));
+}
+
+}  // namespace ash