Don't crash trying to use --snapshot-kind=app-aot from 'dart' rather than 'dart_bootstrap'.
Don't crash trying to use --snapshot-kind=app-aot from 'dart' rather than 'dart_bootstrap'.

R=asiva@google.com

Review URL: https://codereview.chromium.org/2510143002 .

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