[record_use] Correctness: Specify what uris are used

[dcharkes]

The way the tests are set up in the Dart SDK don't yield the same URIs:

$ diff pkg/vm/testcases/transformations/record_use/extension.dart.json.expect pkg/compiler/test/record_use/golden/extension.json.expect

10c10
<       "uri": "extension.dart"
---
>       "uri": "memory:sdk/tests/web/native/extension.dart"

We should set up the tests so that they yield uris that will be seen in the link hooks so that we can document how these uris are formatted in the doc comments correctly.