[CSS Grid Layout] Adapting align-self, align-items and justify-self to the last CSS 3 spec.

Source/core/rendering/RenderFlexibleBox.cpp

 /*
  * Copyright (C) 2011 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 182 matching lines @@
         return baseline;
 
     int marginAscent = direction == HorizontalLine ? marginTop() : marginRight();
     return synthesizedBaselineFromContentBox(this, direction) + marginAscent;
 }
 
 static ItemPosition resolveAlignment(const RenderStyle* parentStyle, const RenderStyle* childStyle)
 {
     ItemPosition align = childStyle->alignSelf();
     if (align == ItemPositionAuto)
-        align = parentStyle->alignItems();
+        align = (parentStyle->alignItems() == ItemPositionAuto) ? ItemPositionStretch : parentStyle->alignItems();
     return align;
 }
 
 void RenderFlexibleBox::removeChild(RenderObject* child)
 {
     RenderBlock::removeChild(child);
     m_intrinsicSizeAlongMainAxis.remove(child);
 }
 
 void RenderFlexibleBox::styleDidChange(StyleDifference diff, const RenderStyle* oldStyle)
@@ skipping 1187 matching lines @@
             ASSERT(child);
             LayoutUnit lineCrossAxisExtent = lineContexts[lineNumber].crossAxisExtent;
             LayoutUnit originalOffset = lineContexts[lineNumber].crossAxisOffset - crossAxisStartEdge;
             LayoutUnit newOffset = contentExtent - originalOffset - lineCrossAxisExtent;
             adjustAlignmentForChild(child, newOffset - originalOffset);
         }
     }
 }
 
 }