Made DSLParser 'expected expression' a fatal error

This matches the behavior of SkSLParser and fixes some spurious
followup errors.

Change-Id: Id1eae353eb6536a6385d04d0426e0de736db6b57
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/444360
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
1 file changed