example-orca: fix lost streamTracerFactor (#9411)

examples/example-orca/src/main/java/io/grpc/examples/orca/CustomBackendMetricsLoadBalancerProvider.java

@@ -124,16 +124,24 @@ final class CustomBackendMetricsLoadBalancerProvider extends LoadBalancerProvide
           return result;
         }
         // Installs ORCA per-query metrics reporting listener.
-        return LoadBalancer.PickResult.withSubchannel(
+        final OrcaPerRequestUtil.OrcaPerRequestReportListener orcaListener =
-            result.getSubchannel(),
-            OrcaPerRequestUtil.getInstance().newOrcaClientStreamTracerFactory(
             new OrcaPerRequestUtil.OrcaPerRequestReportListener() {
           @Override
           public void onLoadReport(MetricReport orcaLoadReport) {
             System.out.println("Example load balancer received per-rpc metrics report:\n"
                 + orcaLoadReport);
           }
-                }));
+        };
+        if (result.getStreamTracerFactory() == null) {
+          return LoadBalancer.PickResult.withSubchannel(
+              result.getSubchannel(),
+              OrcaPerRequestUtil.getInstance().newOrcaClientStreamTracerFactory(orcaListener));
+        } else {
+            return LoadBalancer.PickResult.withSubchannel(
+                result.getSubchannel(),
+                OrcaPerRequestUtil.getInstance().newOrcaClientStreamTracerFactory(
+                    result.getStreamTracerFactory(), orcaListener));
+        }
       }
     }
   }

services/BUILD.bazel

@@ -43,6 +43,7 @@ java_library(
         "//api",
         "//context",
         "@com_google_code_findbugs_jsr305//jar",
+        "@com_google_errorprone_error_prone_annotations//jar",
         "@com_google_guava_guava//jar",
     ],
 )