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

Source/core/css/resolver/StyleAdjuster.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (c) 2011, Code Aurora Forum. All rights reserved.
  * Copyright (C) Research In Motion Limited 2011. All rights reserved.
@@ skipping 277 matching lines @@
     // and to the computed value of align-items on the parent (minus
     // any 'legacy' keywords) on all other boxes.
     if (style.alignSelf() == ItemPositionAuto) {
         if (absolutePositioned) {
             style.setAlignSelf(ItemPositionStretch);
         } else {
             style.setAlignSelf(parentStyle.alignItems());
             style.setAlignSelfOverflowAlignment(parentStyle.alignItemsOverflowAlignment());
         }
     }
+
+    // Block Containers: For table cells, the behavior of the 'auto' depends on the computed
+    // value of 'vertical-align', otherwise behaves as 'start'.
+    // Flex Containers: 'auto' computes to 'flex-start'.
+    // Grid Containers: 'auto' computes to 'start', and 'stretch' behaves like 'start'.
+    if ((style.justifyContent() == ContentPositionAuto) && (style.justifyContentDistribution() == ContentDistributionDefault)) {
+        if (style.isDisplayFlexibleBox()) {
+            style.setJustifyContent(ContentPositionFlexStart);
+        }
+    }
 }
 
 void StyleAdjuster::adjustStyleForTagName(RenderStyle* style, RenderStyle* parentStyle, Element& element)
 {
     // <div> and <span> are the most common elements on the web, we skip all the work for them.
     if (isHTMLDivElement(element) || isHTMLSpanElement(element))
         return;
 
     if (isHTMLTableCellElement(element)) {
         // If we have a <td> that specifies a float property, in quirks mode we just drop the float property.
@@ skipping 141 matching lines @@
     if (style->writingMode() != TopToBottomWritingMode && (style->display() == BOX || style->display() == INLINE_BOX))
         style->setWritingMode(TopToBottomWritingMode);
 
     if (parentStyle->isDisplayFlexibleOrGridBox()) {
         style->setFloating(NoFloat);
         style->setDisplay(equivalentBlockDisplay(style->display(), style->isFloating(), !m_useQuirksModeStyles));
     }
 }
 
 }