Previously the nominal variable builders were created in all cases and
then converted to structural if that was required. It induced some
unnecessary type substitutions and complicated the logic behind the
builders. This CL introduces NominalVariableBuilder and
StructuralVariableBuilder as two possible subclasses of
TypeVariableBuilderBase, and the appropriate builders are created from
start.
This is a follow-up to
https://dart-review.googlesource.com/c/sdk/+/312264
Change-Id: I4e40de158201462dcef96b75445b8f179e1f75b5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/330081
Commit-Queue: Chloe Stefantsova <cstefantsova@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Chloe Stefantsova
9beea1a044