Pass in "mode" to transformer plugins.

sdk/lib/_internal/pub/test/transformer/mode_defaults_to_debug_in_serve_test.dart

Index: sdk/lib/_internal/pub/test/transformer/mode_defaults_to_debug_in_serve_test.dart
diff --git a/sdk/lib/_internal/pub/test/transformer/configuration/configuration_defaults_to_empty_map_test.dart b/sdk/lib/_internal/pub/test/transformer/mode_defaults_to_debug_in_serve_test.dart
similarity index 66%
copy from sdk/lib/_internal/pub/test/transformer/configuration/configuration_defaults_to_empty_map_test.dart
copy to sdk/lib/_internal/pub/test/transformer/mode_defaults_to_debug_in_serve_test.dart
index e84224573756be3b06fd10af820e12416241073f..f45b8da290f554a0ead2b0af4b032547b2df974f 100644
--- a/sdk/lib/_internal/pub/test/transformer/configuration/configuration_defaults_to_empty_map_test.dart
+++ b/sdk/lib/_internal/pub/test/transformer/mode_defaults_to_debug_in_serve_test.dart
@@ -6,9 +6,9 @@ library pub_tests;
 
 import 'dart:convert';
 
-import '../../descriptor.dart' as d;
-import '../../test_pub.dart';
-import '../../serve/utils.dart';
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+import '../serve/utils.dart';
 
 final transformer = """
 import 'dart:async';
@@ -16,17 +16,17 @@ import 'dart:convert';
 
 import 'package:barback/barback.dart';
 
-class ConfigTransformer extends Transformer {
-  final Map configuration;
+class ModeTransformer extends Transformer {
+  final BarbackSettings settings;
 
-  ConfigTransformer.asPlugin(this.configuration);
+  ModeTransformer.asPlugin(this.settings);
 
   String get allowedExtensions => '.txt';
 
   Future apply(Transform transform) {
     return transform.primaryInput.readAsString().then((contents) {
-      var id = transform.primaryInput.id.changeExtension(".json");
-      transform.addOutput(new Asset.fromString(id, JSON.encode(configuration)));
+      transform.addOutput(
+          new Asset.fromString(transform.primaryInput.id, settings.mode.name));
     });
   }
 }
@@ -34,7 +34,7 @@ class ConfigTransformer extends Transformer {
 
 main() {
   initConfig();
-  integration("configuration defaults to an empty map", () {
+  integration("mode defaults to 'debug' in pub serve", () {
     d.dir(appPath, [
       d.pubspec({
         "name": "myapp",
@@ -51,7 +51,7 @@ main() {
     createLockFile('myapp', pkg: ['barback']);
 
     var server = startPubServe();
-    requestShouldSucceed("foo.json", JSON.encode({}));
+    requestShouldSucceed("foo.txt", "debug");
     endPubServe();
   });
 }