Pass in "mode" to transformer plugins.

sdk/lib/_internal/pub/lib/src/command/serve.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library pub.command.serve;
 
 import 'dart:async';
 
+import 'package:barback/barback.dart';
+
 import '../barback/dart_forwarding_transformer.dart';
 import '../barback/dart2js_transformer.dart';
 import '../barback/pub_package_provider.dart';
 import '../barback.dart' as barback;
 import '../command.dart';
 import '../entrypoint.dart';
 import '../exit_codes.dart' as exit_codes;
 import '../io.dart';
 import '../log.dart' as log;
 import '../utils.dart';
@@ skipping 49 matching lines @@
     }).then((graph) {
       // TODO(rnystrom): Add support for dart2dart transformer here.
       var builtInTransformers = null;
       if (useDart2JS) {
         builtInTransformers = [
           new Dart2JSTransformer(graph, minify: minify),
           new DartForwardingTransformer()
         ];
       }
 
-      return barback.createServer(hostname, port, graph,
+      // TODO(rnystrom): Allow specifying other modes.
+      return barback.createServer(hostname, port, graph, BarbackMode.DEBUG,
           builtInTransformers: builtInTransformers);
     }).then((server) {
       /// This completer is used to keep pub running (by not completing) and
       /// to pipe fatal errors to pub's top-level error-handling machinery.
       var completer = new Completer();
 
       server.barback.errors.listen((error) {
         log.error(log.red("Build error:\n$error"));
       });
 
@@ skipping 27 matching lines @@
         if (!completer.isCompleted) completer.completeError(error, stackTrace);
       });
 
       log.message("Serving ${entrypoint.root.name} "
           "on http://$hostname:${server.port}");
 
       return completer.future;
     });
   }
 }