[CSS Grid Layout] Upgrade justify-content parsing to CSS3 Box Alignment spec.

Source/core/css/CSSContentDistributionValue.h

Index: Source/core/css/CSSContentDistributionValue.h
diff --git a/Source/core/css/CSSContentDistributionValue.h b/Source/core/css/CSSContentDistributionValue.h
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+++ b/Source/core/css/CSSContentDistributionValue.h
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+// Copyright (c) 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 CSSContentDistributionValue_h
+#define CSSContentDistributionValue_h
+
+#include "core/css/CSSValue.h"
+#include "core/css/CSSValuePool.h"
+#include "wtf/RefPtr.h"
+
+namespace blink {
+
+class CSSContentDistributionValue : public CSSValue {
+public:
+    static PassRefPtrWillBeRawPtr<CSSContentDistributionValue> create(CSSValueID distribution, CSSValueID position, CSSValueID overflow)
+    {
+        return adoptRefWillBeNoop(new CSSContentDistributionValue(distribution, position, overflow));
+    }
+    ~CSSContentDistributionValue();
+
+    PassRefPtrWillBeRawPtr<CSSPrimitiveValue> distribution() const { return cssValuePool().createIdentifierValue(m_distribution); }
+
+    PassRefPtrWillBeRawPtr<CSSPrimitiveValue> position() const { return cssValuePool().createIdentifierValue(m_position); }
+
+    PassRefPtrWillBeRawPtr<CSSPrimitiveValue> overflow() const { return cssValuePool().createIdentifierValue(m_overflow); }
+
+    String customCSSText() const;
+
+    bool equals(const CSSContentDistributionValue&) const;
+
+    void traceAfterDispatch(Visitor* visitor) { CSSValue::traceAfterDispatch(visitor); }
+
+private:
+    explicit CSSContentDistributionValue(CSSValueID distribution, CSSValueID position, CSSValueID overflow);
+
+    CSSValueID m_distribution;
+    CSSValueID m_position;
+    CSSValueID m_overflow;
+};
+
+DEFINE_CSS_VALUE_TYPE_CASTS(CSSContentDistributionValue, isContentDistributionValue());
+
+} // namespace blink
+
+#endif // CSSContentDistributionValue_h