fields: test that a tagged field takes precedence
fields: test that a tagged field takes precedence

Change-Id: I1d079391f3b7b4d59f4e65a4b7592cd05e6396e0
Reviewed-on: https://code-review.googlesource.com/9564
Reviewed-by: Jun Mukai <7519e7503d434ad998e9a85ea6f0976705697504@google.com>

googleapis/google-cloud-go,googleapis/google-cloud-go,michael-grosshans/google-cloud-go,googleapis/google-cloud-go,michael-grosshans/google-cloud-go,googleapis/google-cloud-go