'SpecParser.java' has always been using an `ANTLRFileStream`, but this
class has been deprecated at this time. Changing the code to use
`CharStreams.fromFileName(...)`.
Change-Id: I35fce3b381ac2e819794c08faef7f97c4c3bea50
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/444840
Commit-Queue: Erik Ernst <eernst@google.com>
Reviewed-by: Chloe Stefantsova <cstefantsova@google.com>
Erik Ernst
57799724ff