Change how desugar finds desugared classes to have it working on Windows

RELNOTES: Change how desugar finds desugared classes to have it working on Windows

--
PiperOrigin-RevId: 149738279
MOS_MIGRATED_REVID=149738279

GitOrigin-RevId: 25df9e962012eb6ac8bf01a031ddf2c257f5cce5
Change-Id: Icf920cf348843403b167a9adfc1fe2f10ac35c57
1 file changed
tree: a69da7e4fc2da3965d2f21016aae45a6ff1af59a
  1. java/