lookupResolvedPackageUris and lookupPackageUris do not handle uris with dart scheme

[annagrin]

calling lookupResolvedPackageUris on dart:html returns null, but according to the vm service protocol it should return a org-dartlang-sdk uri:

https://github.com/dart-lang/sdk/blob/609d31b212baca24d0e769b26b0c1ac4186f11f3/pkg/vm_service/lib/src/vm_service.dart#L932

related: #1446

[annagrin]

Actually fixed in #1458