Refactor RenderThemeChromiumDefault

Source/core/rendering/RenderThemeChromiumLinux.h

+// Copyright 2014 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 RenderThemeChromiumLinux_h
+#define RenderThemeChromiumLinux_h
+
+#include "core/rendering/RenderThemeChromiumDefault.h"
+
+namespace blink {
+
+class RenderThemeChromiumLinux final : public RenderThemeChromiumDefault {
+public:
+    static PassRefPtr<RenderTheme> create();
+    virtual String extraDefaultStyleSheet() override;
+};
+
+} // namespace blink
+
+#endif // RenderThemeChromiumLinux_h