rls: use acceptResolvedAddresses() (#9569)

Switch over from handleResolvedAddresses as part of a LoadBalancer
public API refactoring.

rls/src/main/java/io/grpc/rls/RlsLoadBalancer.java

@@ -49,8 +49,16 @@ final class RlsLoadBalancer extends LoadBalancer {
   }
 
   @Override
-  public void handleResolvedAddresses(ResolvedAddresses resolvedAddresses) {
+  public boolean acceptResolvedAddresses(ResolvedAddresses resolvedAddresses) {
     logger.log(ChannelLogLevel.DEBUG, "Received resolution result: {0}", resolvedAddresses);
+
+    if (resolvedAddresses.getAddresses().isEmpty()) {
+      handleNameResolutionError(Status.UNAVAILABLE.withDescription(
+          "NameResolver returned no usable address. addrs=" + resolvedAddresses.getAddresses()
+              + ", attrs=" + resolvedAddresses.getAttributes()));
+      return false;
+    }
+
     LbPolicyConfiguration lbPolicyConfiguration =
         (LbPolicyConfiguration) resolvedAddresses.getLoadBalancingPolicyConfig();
     checkNotNull(lbPolicyConfiguration, "Missing rls lb config");
@@ -78,6 +86,8 @@ final class RlsLoadBalancer extends LoadBalancer {
       //  not required.
       this.lbPolicyConfiguration = lbPolicyConfiguration;
     }
+
+    return true;
   }
 
   @Override

rls/src/test/java/io/grpc/rls/RlsLoadBalancerTest.java

@@ -445,7 +445,7 @@ public class RlsLoadBalancerTest {
     ConfigOrError parsedConfigOrError =
         provider.parseLoadBalancingPolicyConfig(getServiceConfig());
     assertThat(parsedConfigOrError.getConfig()).isNotNull();
-    rlsLb.handleResolvedAddresses(ResolvedAddresses.newBuilder()
+    rlsLb.acceptResolvedAddresses(ResolvedAddresses.newBuilder()
         .setAddresses(ImmutableList.of(new EquivalentAddressGroup(mock(SocketAddress.class))))
         .setLoadBalancingPolicyConfig(parsedConfigOrError.getConfig())
         .build());