Remove the CSSOM.

sky/engine/core/css/CSSUnknownRule.h

Index: sky/engine/core/css/CSSUnknownRule.h
diff --git a/sky/engine/core/css/CSSUnknownRule.h b/sky/engine/core/css/CSSUnknownRule.h
deleted file mode 100644
index 14e57ea5cf1d34d337ffe70e89d1493d72b80b04..0000000000000000000000000000000000000000
--- a/sky/engine/core/css/CSSUnknownRule.h
+++ /dev/null
@@ -1,41 +0,0 @@
-/*
- * (C) 1999-2003 Lars Knoll (knoll@kde.org)
- * (C) 2002-2003 Dirk Mueller (mueller@kde.org)
- * Copyright (C) 2002, 2006, 2008, 2012 Apple Inc. All rights reserved.
- *
- * This library is free software; you can redistribute it and/or
- * modify it under the terms of the GNU Library General Public
- * License as published by the Free Software Foundation; either
- * version 2 of the License, or (at your option) any later version.
- *
- * This library is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
- * Library General Public License for more details.
- *
- * You should have received a copy of the GNU Library General Public License
- * along with this library; see the file COPYING.LIB.  If not, write to
- * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
- * Boston, MA 02110-1301, USA.
- */
-
-#ifndef SKY_ENGINE_CORE_CSS_CSSUNKNOWNRULE_H_
-#define SKY_ENGINE_CORE_CSS_CSSUNKNOWNRULE_H_
-
-#include "sky/engine/core/css/CSSRule.h"
-
-namespace blink {
-
-class CSSUnknownRule final : public CSSRule {
-public:
-    CSSUnknownRule() : CSSRule(0) { }
-    virtual ~CSSUnknownRule() { }
-
-    virtual CSSRule::Type type() const override { return UNKNOWN_RULE; }
-    virtual String cssText() const override { return String(); }
-    virtual void reattach(StyleRuleBase*) override { }
-};
-
-} // namespace blink
-
-#endif  // SKY_ENGINE_CORE_CSS_CSSUNKNOWNRULE_H_