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

Source/core/rendering/style/RenderStyleConstants.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
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     OverflowAlignmentDefault,
     OverflowAlignmentTrue,
     OverflowAlignmentSafe
 };
 
 enum ItemPositionType {
     NonLegacyPosition,
     LegacyPosition
 };
 
+enum ContentPosition {
+    ContentPositionAuto,
+    ContentPositionBaseline,
+    ContentPositionLastBaseline,
+    ContentPositionCenter,
+    ContentPositionStart,
+    ContentPositionEnd,
+    ContentPositionFlexStart,
+    ContentPositionFlexEnd,
+    ContentPositionLeft,
+    ContentPositionRight
+};
+
+enum ContentDistributionType {
+    ContentDistributionDefault,
+    ContentDistributionSpaceBetween,
+    ContentDistributionSpaceAround,
+    ContentDistributionSpaceEvenly,
+    ContentDistributionStretch
+};
+
 // Reasonable maximum to prevent insane font sizes from causing crashes on some platforms (such as Windows).
 static const float maximumAllowedFontSize = 1000000.0f;
 
 enum TextIndentLine { TextIndentFirstLine, TextIndentEachLine };
 enum TextIndentType { TextIndentNormal, TextIndentHanging };
 
 enum CSSBoxType { BoxMissing = 0, MarginBox, BorderBox, PaddingBox, ContentBox };
 
 } // namespace blink
 
 #endif // RenderStyleConstants_h