This problem is caused by lack of support for view reference fields in
Item_ref::resolved_used_tables(). We have a query fragment like this:

  select 1 from v2
  where 1 = (select 1 from t1 group by v2.a)

This fragment is part of a subquery that is transformed into a semi-join.
During that transformation, fix_after_pullout() is called, which calls
upon resolved_used_tables() to re-calculate used tables information
for the scalar subquery. v2.a is a reference to a const value in
the view definition. However, Item_ref::resolved_used_tables() expects
to see a FIELD_ITEM, and asserts when it does not.

The fix for this problem is to accept that Item_direct_view_ref may
reference other expressions than just fields and call
resolved_used_tables() on the referenced expression.

sql/item.cc
  In Item_ref::resolved_used_tables(), noticed that the referenced item's
  type need not be a FIELD_ITEM when item is Item_direct_view_ref.

sql/item.h
  Moved resolved_used_tables() from class Item_ident to class Item,
  and let the default implementation call used_tables().
  Emphasized that resolved_used_tables() behaves like used_tables() except
  for fields, and that Item::resolved_used_tables() is for internal use.