Show subdirectories in test migration progress report.
Show subdirectories in test migration progress report.

Change-Id: I2b7c059030d0c5a87d074e37c86f7532c302ff9c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/130963
Auto-Submit: Bob Nystrom <afede3a9ebedb865bee78398feff6fbe97068f17@google.com>
Reviewed-by: Nicholas Shahan <03847abd2d8aadfe859ecb98095a31f9f515dc47@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk