Migrate from PARSER to parser() as a way of getting the parser of a protobuf message.

This was done by #587 (commit af9fb6de77107d817bf69cdb9e45e235a76dd8bd)
but was accidentally reverted by commit 73acc73dbf53171ab6d6126d1eb1e76e9ce81171.
diff --git a/compiler/src/java_plugin/cpp/java_generator.cpp b/compiler/src/java_plugin/cpp/java_generator.cpp
index bac19ca..54eb8f3 100644
--- a/compiler/src/java_plugin/cpp/java_generator.cpp
+++ b/compiler/src/java_plugin/cpp/java_generator.cpp
@@ -122,8 +122,8 @@
           "    $MethodDescriptor$.create(\n"
           "        $MethodType$.$method_type$,\n"
           "        \"$Package$$service_name$\", \"$method_name$\",\n"
-          "        $ProtoUtils$.marshaller($input_type$.PARSER),\n"
-          "        $ProtoUtils$.marshaller($output_type$.PARSER));\n");
+          "        $ProtoUtils$.marshaller($input_type$.parser()),\n"
+          "        $ProtoUtils$.marshaller($output_type$.parser()));\n");
     }
   }
   p->Print("\n");
diff --git a/compiler/src/test/golden/TestService.java.txt b/compiler/src/test/golden/TestService.java.txt
index 13d92f3..5d6dae0 100644
--- a/compiler/src/test/golden/TestService.java.txt
+++ b/compiler/src/test/golden/TestService.java.txt
@@ -21,40 +21,40 @@
       io.grpc.MethodDescriptor.create(
           io.grpc.MethodDescriptor.MethodType.UNARY,
           "grpc.testing.TestService", "UnaryCall",
-          io.grpc.protobuf.ProtoUtils.marshaller(io.grpc.testing.integration.Test.SimpleRequest.PARSER),
-          io.grpc.protobuf.ProtoUtils.marshaller(io.grpc.testing.integration.Test.SimpleResponse.PARSER));
+          io.grpc.protobuf.ProtoUtils.marshaller(io.grpc.testing.integration.Test.SimpleRequest.parser()),
+          io.grpc.protobuf.ProtoUtils.marshaller(io.grpc.testing.integration.Test.SimpleResponse.parser()));
   // Static method descriptors that strictly reflect the proto.
   public static final io.grpc.MethodDescriptor<io.grpc.testing.integration.Test.StreamingOutputCallRequest,
       io.grpc.testing.integration.Test.StreamingOutputCallResponse> METHOD_STREAMING_OUTPUT_CALL =
       io.grpc.MethodDescriptor.create(
           io.grpc.MethodDescriptor.MethodType.SERVER_STREAMING,
           "grpc.testing.TestService", "StreamingOutputCall",
-          io.grpc.protobuf.ProtoUtils.marshaller(io.grpc.testing.integration.Test.StreamingOutputCallRequest.PARSER),
-          io.grpc.protobuf.ProtoUtils.marshaller(io.grpc.testing.integration.Test.StreamingOutputCallResponse.PARSER));
+          io.grpc.protobuf.ProtoUtils.marshaller(io.grpc.testing.integration.Test.StreamingOutputCallRequest.parser()),
+          io.grpc.protobuf.ProtoUtils.marshaller(io.grpc.testing.integration.Test.StreamingOutputCallResponse.parser()));
   // Static method descriptors that strictly reflect the proto.
   public static final io.grpc.MethodDescriptor<io.grpc.testing.integration.Test.StreamingInputCallRequest,
       io.grpc.testing.integration.Test.StreamingInputCallResponse> METHOD_STREAMING_INPUT_CALL =
       io.grpc.MethodDescriptor.create(
           io.grpc.MethodDescriptor.MethodType.CLIENT_STREAMING,
           "grpc.testing.TestService", "StreamingInputCall",
-          io.grpc.protobuf.ProtoUtils.marshaller(io.grpc.testing.integration.Test.StreamingInputCallRequest.PARSER),
-          io.grpc.protobuf.ProtoUtils.marshaller(io.grpc.testing.integration.Test.StreamingInputCallResponse.PARSER));
+          io.grpc.protobuf.ProtoUtils.marshaller(io.grpc.testing.integration.Test.StreamingInputCallRequest.parser()),
+          io.grpc.protobuf.ProtoUtils.marshaller(io.grpc.testing.integration.Test.StreamingInputCallResponse.parser()));
   // Static method descriptors that strictly reflect the proto.
   public static final io.grpc.MethodDescriptor<io.grpc.testing.integration.Test.StreamingOutputCallRequest,
       io.grpc.testing.integration.Test.StreamingOutputCallResponse> METHOD_FULL_DUPLEX_CALL =
       io.grpc.MethodDescriptor.create(
           io.grpc.MethodDescriptor.MethodType.DUPLEX_STREAMING,
           "grpc.testing.TestService", "FullDuplexCall",
-          io.grpc.protobuf.ProtoUtils.marshaller(io.grpc.testing.integration.Test.StreamingOutputCallRequest.PARSER),
-          io.grpc.protobuf.ProtoUtils.marshaller(io.grpc.testing.integration.Test.StreamingOutputCallResponse.PARSER));
+          io.grpc.protobuf.ProtoUtils.marshaller(io.grpc.testing.integration.Test.StreamingOutputCallRequest.parser()),
+          io.grpc.protobuf.ProtoUtils.marshaller(io.grpc.testing.integration.Test.StreamingOutputCallResponse.parser()));
   // Static method descriptors that strictly reflect the proto.
   public static final io.grpc.MethodDescriptor<io.grpc.testing.integration.Test.StreamingOutputCallRequest,
       io.grpc.testing.integration.Test.StreamingOutputCallResponse> METHOD_HALF_DUPLEX_CALL =
       io.grpc.MethodDescriptor.create(
           io.grpc.MethodDescriptor.MethodType.DUPLEX_STREAMING,
           "grpc.testing.TestService", "HalfDuplexCall",
-          io.grpc.protobuf.ProtoUtils.marshaller(io.grpc.testing.integration.Test.StreamingOutputCallRequest.PARSER),
-          io.grpc.protobuf.ProtoUtils.marshaller(io.grpc.testing.integration.Test.StreamingOutputCallResponse.PARSER));
+          io.grpc.protobuf.ProtoUtils.marshaller(io.grpc.testing.integration.Test.StreamingOutputCallRequest.parser()),
+          io.grpc.protobuf.ProtoUtils.marshaller(io.grpc.testing.integration.Test.StreamingOutputCallResponse.parser()));
 
   public static TestServiceStub newStub(io.grpc.Channel channel) {
     return new TestServiceStub(channel, CONFIG);