[pkg/vm_service] fix to analysis warnings about required arguments
[pkg/vm_service] fix to analysis warnings about required arguments

Change-Id: I752d0d09b9cee234fe9e8c06144f210eb9a5bb55
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/162401
Reviewed-by: Ben Konyi <67ffcaedcc3dc3d87dddb9627b72dd41756b31b1@google.com>
Commit-Queue: Devon Carew <e996497f4f2225f0ee7a9f4d1696ee710b488b66@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