[dartdevc] fix ddb directories and source maps
[dartdevc] fix ddb directories and source maps

With this change, one can launch tests, e.g.,

> ddb -r chrome -d -k tests/compiler/dartdevc_native/subtype_test.dart

and step through Dart SDK code using source maps.

Change-Id: I1662a4df76d29e3ccb80a4754147839da784ebe6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/107480
Auto-Submit: Vijay Menon <671ecbb18d31a1c038875027dcfe976af959ea9f@google.com>
Reviewed-by: Nicholas Shahan <03847abd2d8aadfe859ecb98095a31f9f515dc47@google.com>
Commit-Queue: Vijay Menon <671ecbb18d31a1c038875027dcfe976af959ea9f@google.com>

dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk