Debug why dynamic/list/var fails to JSON parse correctly

[TristonianJones]

For some reason the following input parses fine within the gRPC based conformance stacks, but does not properly deserialize within the pipe-based protocol used for C++:

test {
    name: "var"
    expr: "x"
    type_env {
      name: "x"
      ident { type { message_type: "google.protobuf.ListValue" } }
    }
    bindings {
      key: "x"
      value {
        value {
          object_value {
            [type.googleapis.com/google.protobuf.ListValue] {
              values { string_value: "bar" }
              values {
                list_value {
                  values { string_value: "a" }
                  values { string_value: "b" }
                }
              }
            }
          }
        }
      }
    }
    value {
      list_value {
        values { string_value: "bar" }
        values {
          list_value {
            values { string_value: "a" }
            values { string_value: "b" }
          }
        }
      }
    }
  }