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

Source/core/rendering/RenderFullScreen.cpp

 /*
  * Copyright (C) 2010 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *     notice, this list of conditions and the following disclaimer in the
@@ skipping 81 matching lines @@
 {
     RefPtr<RenderStyle> fullscreenStyle = RenderStyle::createDefaultStyle();
 
     // Create a stacking context:
     fullscreenStyle->setZIndex(INT_MAX);
 
     fullscreenStyle->setFontDescription(FontDescription());
     fullscreenStyle->font().update(nullptr);
 
     fullscreenStyle->setDisplay(FLEX);
-    fullscreenStyle->setJustifyContent(JustifyCenter);
+    fullscreenStyle->setJustifyContent(ContentPositionCenter);
     fullscreenStyle->setAlignItems(ItemPositionCenter);
     fullscreenStyle->setFlexDirection(FlowColumn);
 
     fullscreenStyle->setPosition(FixedPosition);
     fullscreenStyle->setWidth(Length(100.0, Percent));
     fullscreenStyle->setHeight(Length(100.0, Percent));
     fullscreenStyle->setLeft(Length(0, blink::Fixed));
     fullscreenStyle->setTop(Length(0, blink::Fixed));
 
     fullscreenStyle->setBackgroundColor(StyleColor(Color::black));
@@ skipping 80 matching lines @@
     if (!m_placeholder) {
         m_placeholder = new RenderFullScreenPlaceholder(this);
         m_placeholder->setStyle(style);
         if (parent()) {
             parent()->addChild(m_placeholder, this);
             parent()->setNeedsLayoutAndPrefWidthsRecalcAndFullPaintInvalidation();
         }
     } else
         m_placeholder->setStyle(style);
 }