Reland main thread position sticky implementation.

third_party/WebKit/Source/core/layout/LayoutFlexibleBox.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 291 matching lines @@
         layoutPositionedObjects(relayoutChildren || isDocumentElement());
 
         // FIXME: css3/flexbox/repaint-rtl-column.html seems to issue paint invalidations for more overflow than it needs to.
         computeOverflow(clientLogicalBottomAfterRepositioning());
     }
 
     updateLayerTransformAfterLayout();
 
     // Update our scroll information if we're overflow:auto/scroll/hidden now that we know if
     // we overflow or not.
-    updateScrollInfoAfterLayout();
+    updateAfterLayout();
 
     clearNeedsLayout();
 }
 
 void LayoutFlexibleBox::paintChildren(const PaintInfo& paintInfo, const LayoutPoint& paintOffset) const
 {
     BlockPainter::paintChildrenOfFlexibleBox(*this, paintInfo, paintOffset);
 }
 
 void LayoutFlexibleBox::repositionLogicalHeightDependentFlexItems(Vector<LineContext>& lineContexts)
@@ skipping 1455 matching lines @@
             ASSERT(child);
             LayoutUnit lineCrossAxisExtent = lineContexts[lineNumber].crossAxisExtent;
             LayoutUnit originalOffset = lineContexts[lineNumber].crossAxisOffset - crossAxisStartEdge;
             LayoutUnit newOffset = contentExtent - originalOffset - lineCrossAxisExtent;
             adjustAlignmentForChild(*child, newOffset - originalOffset);
         }
     }
 }
 
 } // namespace blink