c390eb0931
This adds an InternalLegacyVariable the doesn't derive from LegacyVariable. This fully separates InternalVariable from Variable and assigned variable tracking and flow analysis is now changed to used InternalVariable instead. TEST=existing Change-Id: Ida9dc78d4f0e3fab3baf7a965273e1ddf68a80b8 Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/510341 Reviewed-by: Chloe Stefantsova <cstefantsova@google.com> Reviewed-by: Alexander Markov <alexmarkov@google.com>