[ Service ] Fix cast error in _decodeAssets return value
[ Service ] Fix cast error in _decodeAssets return value

Change-Id: I03da2a2e37582e3ec2cd4c2233d5e7cbca0071f0
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/240303
Reviewed-by: Ryan Macnak <d738b7f001baf9789095d7dc549cff6de60b011d@google.com>
Commit-Queue: Ben Konyi <67ffcaedcc3dc3d87dddb9627b72dd41756b31b1@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