Mark generated abstract class as Experimental

benchmarks/src/generated/main/grpc/io/grpc/benchmarks/proto/BenchmarkServiceGrpc.java

@@ -67,6 +67,7 @@ public class BenchmarkServiceGrpc {
         io.grpc.stub.StreamObserver<io.grpc.benchmarks.proto.Messages.SimpleResponse> responseObserver);
   }
 
+  @io.grpc.ExperimentalApi
   public static abstract class AbstractBenchmarkService implements BenchmarkService, io.grpc.BindableService {
 
     @java.lang.Override

benchmarks/src/generated/main/grpc/io/grpc/benchmarks/proto/WorkerServiceGrpc.java

@@ -91,6 +91,7 @@ public class WorkerServiceGrpc {
         io.grpc.stub.StreamObserver<io.grpc.benchmarks.proto.Control.Void> responseObserver);
   }
 
+  @io.grpc.ExperimentalApi
   public static abstract class AbstractWorkerService implements WorkerService, io.grpc.BindableService {
 
     @java.lang.Override

compiler/src/java_plugin/cpp/java_generator.cpp

@@ -297,6 +297,7 @@ static void PrintStub(
   if (abstract) {
     p->Print(
         *vars,
+        "@$ExperimentalApi$\n"
         "public static abstract class $abstract_name$ implements $service_name$, "
         "$BindableService$ {\n");
   } else if (!impl) {

compiler/src/test/golden/TestService.java.txt

@@ -103,6 +103,7 @@ public class TestServiceGrpc {
         io.grpc.stub.StreamObserver<io.grpc.testing.integration.Test.StreamingOutputCallResponse> responseObserver);
   }
 
+  @io.grpc.ExperimentalApi
   public static abstract class AbstractTestService implements TestService, io.grpc.BindableService {
 
     @java.lang.Override

compiler/src/testLite/golden/TestService.java.txt

@@ -103,6 +103,7 @@ public class TestServiceGrpc {
         io.grpc.stub.StreamObserver<io.grpc.testing.integration.Test.StreamingOutputCallResponse> responseObserver);
   }
 
+  @io.grpc.ExperimentalApi
   public static abstract class AbstractTestService implements TestService, io.grpc.BindableService {
 
     @java.lang.Override

compiler/src/testNano/golden/TestService.java.txt

@@ -181,6 +181,7 @@ public class TestServiceGrpc {
         io.grpc.stub.StreamObserver<io.grpc.testing.integration.nano.Test.StreamingOutputCallResponse> responseObserver);
   }
 
+  @io.grpc.ExperimentalApi
   public static abstract class AbstractTestService implements TestService, io.grpc.BindableService {
 
     @java.lang.Override

examples/src/generated/main/grpc/io/grpc/examples/helloworld/GreeterGrpc.java

@@ -55,6 +55,7 @@ public class GreeterGrpc {
         io.grpc.stub.StreamObserver<io.grpc.examples.helloworld.HelloReply> responseObserver);
   }
 
+  @io.grpc.ExperimentalApi
   public static abstract class AbstractGreeter implements Greeter, io.grpc.BindableService {
 
     @java.lang.Override

examples/src/generated/main/grpc/io/grpc/examples/routeguide/RouteGuideGrpc.java

@@ -91,6 +91,7 @@ public class RouteGuideGrpc {
         io.grpc.stub.StreamObserver<io.grpc.examples.routeguide.RouteNote> responseObserver);
   }
 
+  @io.grpc.ExperimentalApi
   public static abstract class AbstractRouteGuide implements RouteGuide, io.grpc.BindableService {
 
     @java.lang.Override

grpclb/src/generated/main/grpc/io/grpc/grpclb/LoadBalancerGrpc.java

@@ -55,6 +55,7 @@ public class LoadBalancerGrpc {
         io.grpc.stub.StreamObserver<io.grpc.grpclb.LoadBalanceResponse> responseObserver);
   }
 
+  @io.grpc.ExperimentalApi
   public static abstract class AbstractLoadBalancer implements LoadBalancer, io.grpc.BindableService {
 
     @java.lang.Override

interop-testing/src/generated/main/grpc/io/grpc/testing/integration/MetricsServiceGrpc.java

@@ -67,6 +67,7 @@ public class MetricsServiceGrpc {
         io.grpc.stub.StreamObserver<io.grpc.testing.integration.Metrics.GaugeResponse> responseObserver);
   }
 
+  @io.grpc.ExperimentalApi
   public static abstract class AbstractMetricsService implements MetricsService, io.grpc.BindableService {
 
     @java.lang.Override

interop-testing/src/generated/main/grpc/io/grpc/testing/integration/ReconnectServiceGrpc.java

@@ -67,6 +67,7 @@ public class ReconnectServiceGrpc {
         io.grpc.stub.StreamObserver<io.grpc.testing.integration.Messages.ReconnectInfo> responseObserver);
   }
 
+  @io.grpc.ExperimentalApi
   public static abstract class AbstractReconnectService implements ReconnectService, io.grpc.BindableService {
 
     @java.lang.Override

interop-testing/src/generated/main/grpc/io/grpc/testing/integration/TestServiceGrpc.java

@@ -115,6 +115,7 @@ public class TestServiceGrpc {
         io.grpc.stub.StreamObserver<io.grpc.testing.integration.Messages.StreamingOutputCallResponse> responseObserver);
   }
 
+  @io.grpc.ExperimentalApi
   public static abstract class AbstractTestService implements TestService, io.grpc.BindableService {
 
     @java.lang.Override

interop-testing/src/generated/main/grpc/io/grpc/testing/integration/UnimplementedServiceGrpc.java

@@ -55,6 +55,7 @@ public class UnimplementedServiceGrpc {
         io.grpc.stub.StreamObserver<com.google.protobuf.EmptyProtos.Empty> responseObserver);
   }
 
+  @io.grpc.ExperimentalApi
   public static abstract class AbstractUnimplementedService implements UnimplementedService, io.grpc.BindableService {
 
     @java.lang.Override