[Experimental] Implement some part of custom properties in style maps

third_party/WebKit/Source/core/css/CSSComputedStyleDeclaration.h

 /*
  * Copyright (C) 2004 Zack Rusin <zack@kde.org>
  * Copyright (C) 2004, 2005, 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 Lesser 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,
@@ skipping 30 matching lines @@
 class CORE_EXPORT CSSComputedStyleDeclaration final
     : public CSSStyleDeclaration {
  public:
   static CSSComputedStyleDeclaration* create(
       Node* node,
       bool allowVisitedStyle = false,
       const String& pseudoElementName = String()) {
     return new CSSComputedStyleDeclaration(node, allowVisitedStyle,
                                            pseudoElementName);
   }
+
+  static const Vector<CSSPropertyID>& computableProperties();
   ~CSSComputedStyleDeclaration() override;
 
   String getPropertyValue(CSSPropertyID) const;
   bool getPropertyPriority(CSSPropertyID) const;
 
   MutableStylePropertySet* copyProperties() const;
 
   const CSSValue* getPropertyCSSValue(CSSPropertyID) const;
   const CSSValue* getPropertyCSSValue(AtomicString customPropertyName) const;
   std::unique_ptr<HashMap<AtomicString, RefPtr<CSSVariableData>>> getVariables()
@@ skipping 50 matching lines @@
   bool cssPropertyMatches(CSSPropertyID, const CSSValue*) const override;
 
   Member<Node> m_node;
   PseudoId m_pseudoElementSpecifier;
   bool m_allowVisitedStyle;
 };
 
 }  // namespace blink
 
 #endif  // CSSComputedStyleDeclaration_h