aura: Make aura::TooltipClient completely static?

ui/views/test/test_tooltip_client.h

-// Copyright (c) 2011 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 UI_AURA_TEST_TEST_TOOLTIP_CLIENT_H_
-#define UI_AURA_TEST_TEST_TOOLTIP_CLIENT_H_
-#pragma once
-
-#include "base/compiler_specific.h"
-#include "ui/aura/client/tooltip_client.h"
-
-namespace aura {
-class Window;
-
-namespace test {
-
-class TestTooltipClient : public TooltipClient {
- public:
-  TestTooltipClient();
-  virtual ~TestTooltipClient();
-
- private:
-  // Overridden from TooltipClient:
-  virtual void UpdateTooltip(Window* target) OVERRIDE {}
-
-  DISALLOW_COPY_AND_ASSIGN(TestTooltipClient);
-};
-
-}  // namespace test
-}  // namespace aura
-
-#endif  // UI_AURA_TEST_TEST_TOOLTIP_CLIENT_H_