Commits on Mar 11, 2020

1. layout_2020: Paint hoisted positioned fragments in tree order …

   Instead of painting hoisted position fragments in the order to which
   they are hoisted, paint them in tree order and properly incorporate them
   into the stacking context.
   
   We do this by creating a placeholder fragment in the original tree position
   of hoisted fragments. The ghost fragment contains an atomic id which
   links back to the hoisted fragment in the containing block.
   
   While building the stacking context, we keep track of containing blocks
   and their children. When encountering a placeholder fragment we look at
   the containing block's hoisted children in order to properly paint the
   hoisted fragment.
   
   One notable design modification in this change is that hoisted fragments
   no longer need an AnonymousFragment as their parent. Instead they are
   now direct children of the fragment that establishes their containing block.

   

   mrobinson committed Mar 11, 2020

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