code: public final Policy setIamPolicy(String resource, Policy policy) {
  
      SetIamPolicyRequest request =
          SetIamPolicyRequest.newBuilder().setResource(resource).setPolicy(policy).build();
      return setIamPolicy(request);
    }
docs: Sets the access control policy on an instance resource. Replaces any existing policy.
  
  <p>Authorization requires `spanner.instances.setIamPolicy` on
  [resource][google.iam.v1.SetIamPolicyRequest.resource].
  
  <p>Sample code:
  
  <pre><code>
  try (InstanceAdminClient instanceAdminClient = InstanceAdminClient.create()) {
  String formattedResource = InstanceName.format("[PROJECT]", "[INSTANCE]");
  Policy policy = Policy.newBuilder().build();
  Policy response = instanceAdminClient.setIamPolicy(formattedResource, policy);
  }
  </code></pre>
  
  @param resource REQUIRED: The resource for which the policy is being specified. `resource` is
  usually specified as a path. For example, a Project resource is specified as
  `projects/{project}`.
  @param policy REQUIRED: The complete policy to be applied to the `resource`. The size of the
  policy is limited to a few 10s of KB. An empty policy is a valid policy but certain Cloud
  Platform services (such as Projects) might reject them.
  @throws com.google.api.gax.rpc.ApiException if the remote call fails