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

Source/core/css/CSSContentDistributionValue.cpp

+// 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.
+
+#include "config.h"
+#include "core/css/CSSContentDistributionValue.h"
+
+#include "core/css/CSSValueList.h"
+#include "wtf/text/StringBuilder.h"
+
+namespace blink {
+
+CSSContentDistributionValue::CSSContentDistributionValue(CSSValueID distribution, CSSValueID position, CSSValueID overflow)
+    : CSSValue(CSSContentDistributionClass)
+    , m_distribution(distribution)
+    , m_position(position)
+    , m_overflow(overflow)
+{
+}
+
+CSSContentDistributionValue::~CSSContentDistributionValue()
+{
+}
+
+String CSSContentDistributionValue::customCSSText() const
+{
+    RefPtrWillBeRawPtr<CSSValueList> list = CSSValueList::createSpaceSeparated();
+
+    if (m_distribution != CSSValueInvalid)
+        list->append(distribution());
+    if (m_position != CSSValueInvalid)
+        list->append(position());
+    if (m_overflow != CSSValueInvalid)
+        list->append(overflow());
+
+    return list.release()->customCSSText();
+}
+
+bool CSSContentDistributionValue::equals(const CSSContentDistributionValue& other) const
+{
+    return m_distribution == other.m_distribution && m_position == other.m_position && m_overflow == other.m_overflow;
+}
+
+}