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

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

Index: third_party/WebKit/Source/core/css/CSSPendingSubstitutionValue.h
diff --git a/third_party/WebKit/Source/core/css/CSSPendingSubstitutionValue.h b/third_party/WebKit/Source/core/css/CSSPendingSubstitutionValue.h
new file mode 100644
index 0000000000000000000000000000000000000000..736ed647a07f379b99b709c32efac1d11c7f35ef
--- /dev/null
+++ b/third_party/WebKit/Source/core/css/CSSPendingSubstitutionValue.h
@@ -0,0 +1,51 @@
+// Copyright 2016 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 CSSPendingSubstitutionValue_h
+#define CSSPendingSubstitutionValue_h
+
+#include "core/CSSPropertyNames.h"
+#include "core/css/CSSValue.h"
+#include "core/css/CSSVariableReferenceValue.h"
+
+namespace blink {
+
+class CSSPendingSubstitutionValue : public CSSValue {
+public:
+    static CSSPendingSubstitutionValue* create(CSSPropertyID shorthandPropertyId, CSSVariableReferenceValue* shorthandValue)
+    {
+        return new CSSPendingSubstitutionValue(shorthandPropertyId, shorthandValue);
+    }
+
+    CSSVariableReferenceValue* shorthandValue() const
+    {
+        return m_shorthandValue.get();
+    }
+
+    CSSPropertyID shorthandPropertyId() const
+    {
+        return m_shorthandPropertyId;
+    }
+
+    bool equals(const CSSPendingSubstitutionValue& other) const { return m_shorthandValue == other.m_shorthandValue; }
+    String customCSSText() const;
+
+    DECLARE_TRACE_AFTER_DISPATCH();
+private:
+    CSSPendingSubstitutionValue(CSSPropertyID shorthandPropertyId, CSSVariableReferenceValue* shorthandValue)
+        : CSSValue(PendingSubstitutionValueClass)
+        , m_shorthandPropertyId(shorthandPropertyId)
+        , m_shorthandValue(shorthandValue)
+    {
+    }
+
+    CSSPropertyID m_shorthandPropertyId;
+    Member<CSSVariableReferenceValue> m_shorthandValue;
+};
+
+DEFINE_CSS_VALUE_TYPE_CASTS(CSSPendingSubstitutionValue, isPendingSubstitutionValue());
+
+} // namespace blink
+
+#endif // CSSPendingSubstitutionValue_h