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

Source/core/rendering/RenderGrid.cpp

 /*
  * Copyright (C) 2011 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 1201 matching lines @@
     LayoutUnit endOfRow = m_rowPositions[coordinate.rows.resolvedFinalPosition.next().toInt()];
 
     // FIXME: This should account for the grid item's <overflow-position>.
     return startOfRow + std::max<LayoutUnit>(0, endOfRow - startOfRow - child->logicalHeight()) / 2;
 }
 
 // FIXME: We should move this logic to the StyleAdjuster or the StyleBuilder.
 static ItemPosition resolveAlignment(const RenderStyle* parentStyle, const RenderStyle* childStyle)
 {
     ItemPosition align = childStyle->alignSelf();
-    // The auto keyword computes to the computed value of align-items on the parent.
+    // The auto keyword computes to the parent's align-items computed value, or to "stretch", if not set or "auto".
     if (align == ItemPositionAuto)
         align = (parentStyle->alignItems() == ItemPositionAuto) ? ItemPositionStretch : parentStyle->alignItems();
     return align;
 }
 
 LayoutUnit RenderGrid::rowPositionForChild(const RenderBox* child) const
 {
     bool hasOrthogonalWritingMode = child->isHorizontalWritingMode() != isHorizontalWritingMode();
     ItemPosition alignSelf = resolveAlignment(style(), child->style());
 
@@ skipping 145 matching lines @@
     if (isOutOfFlowPositioned())
         return "RenderGrid (positioned)";
     if (isAnonymous())
         return "RenderGrid (generated)";
     if (isRelPositioned())
         return "RenderGrid (relative positioned)";
     return "RenderGrid";
 }
 
 } // namespace blink