Add expansion of shorthands with custom properties to longhands using a pending substition value.

third_party/WebKit/Source/core/css/resolver/StyleResolverState.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 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,
@@ skipping 142 matching lines @@
         if (m_style->setTextOrientation(textOrientation))
             m_fontBuilder.didChangeTextOrientation();
     }
 
     void setHasDirAutoAttribute(bool value) { m_hasDirAutoAttribute = value; }
     bool hasDirAutoAttribute() const { return m_hasDirAutoAttribute; }
 
     void setCustomPropertySetForApplyAtRule(const String&, StylePropertySet*);
     StylePropertySet* customPropertySetForApplyAtRule(const String&);
 
+    void setCssValueForLonghandPropertyId(CSSPropertyID, const CSSValue*);

[Timothy Loh, 2016/06/22 00:06:12]

Css -> CSS

[Andy Mutton, 2016/06/24 04:53:26]

Blurgh! Done.

+    const CSSValue* cssValueForLonghandPropertyId(CSSPropertyID);
+
 private:
     ElementResolveContext m_elementContext;
     Member<Document> m_document;
 
     // m_style is the primary output for each element's style resolve.
     RefPtr<ComputedStyle> m_style;
 
     CSSToLengthConversionData m_cssToLengthConversionData;
 
     // m_parentStyle is not always just ElementResolveContext::parentStyle,
     // so we keep it separate.
     RefPtr<ComputedStyle> m_parentStyle;
 
     CSSAnimationUpdate m_animationUpdate;
 
     bool m_applyPropertyToRegularStyle;
     bool m_applyPropertyToVisitedLinkStyle;
     bool m_hasDirAutoAttribute;
 
     FontBuilder m_fontBuilder;
 
     std::unique_ptr<CachedUAStyle> m_cachedUAStyle;
 
     ElementStyleResources m_elementStyleResources;
 
     HeapHashMap<String, Member<StylePropertySet>> m_customPropertySetsForApplyAtRule;
+
+    HeapHashMap<CSSPropertyID, Member<const CSSValue>> m_parsedLonghandCssValueForVariableResolver;

[Timothy Loh, 2016/06/22 00:06:12]

I think this is insufficient for cases like:

$0.style.cssText = '--b1: 10px solid grey; --b2: 20px dashed green; border:
var(--b1); border-right: var(--b2);'

Firefox correctly renders (grey border, green dashed for right border), but I
think we'll get this wrong with this patch.

[Andy Mutton, 2016/06/24 04:53:26]

Done. Weird, more complicated caching structure added. Happy to change any bits
of it that look funky!

 };
 
 } // namespace blink
 
 #endif // StyleResolverState_h