Fix unchecked operation warnings in FlutterMain (#9073)

Also remove trailing whitespace on some lines
https://dart.googlesource.com/external/github.com/flutter/engine/+/ee6a9c40492e54a0ae160293900d9e3b42b725d7
1 file changed
tree: 9e27558a7ea71638a80522ff7c7c365349140277
  1. commits.json