mash: Port TrayUpdateTest to AshTest

ash/common/test/wm_shell_test_api.h

Index: ash/common/test/wm_shell_test_api.h
diff --git a/ash/common/test/wm_shell_test_api.h b/ash/common/test/wm_shell_test_api.h
new file mode 100644
index 0000000000000000000000000000000000000000..07ab6fff2e916e0978fb233de0b52d38f41418fb
--- /dev/null
+++ b/ash/common/test/wm_shell_test_api.h
@@ -0,0 +1,30 @@
+// 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.
+
+#ifndef ASH_COMMON_TEST_WM_SHELL_TEST_API_H_
+#define ASH_COMMON_TEST_WM_SHELL_TEST_API_H_
+
+#include <memory>
+
+#include "base/macros.h"
+
+namespace ash {
+
+class SystemTrayDelegate;
+
+// Test API to access the internal state of the singleton WmShell.
+class WmShellTestApi {
+ public:
+  WmShellTestApi();
+  ~WmShellTestApi();
+
+  void SetSystemTrayDelegate(std::unique_ptr<SystemTrayDelegate> delegate);
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(WmShellTestApi);
+};
+
+}  // namespace ash
+
+#endif  // ASH_COMMON_TEST_WM_SHELL_TEST_API_H_