Default to "127.0.0.1" in pub serve.

sdk/lib/_internal/pub/lib/src/barback/load_transformers.dart

Index: sdk/lib/_internal/pub/lib/src/barback/load_transformers.dart
diff --git a/sdk/lib/_internal/pub/lib/src/barback/load_transformers.dart b/sdk/lib/_internal/pub/lib/src/barback/load_transformers.dart
index fe4449f82cf8d12009389c266851fd6616bfe93b..7c86a677a400618cdc4242f9bf37ffbc4d3267b2 100644
--- a/sdk/lib/_internal/pub/lib/src/barback/load_transformers.dart
+++ b/sdk/lib/_internal/pub/lib/src/barback/load_transformers.dart
@@ -6,6 +6,7 @@ library pub.load_transformers;
 
 import 'dart:async';
 import 'dart:convert';
+import 'dart:io';
 import 'dart:isolate';
 
 import 'package:barback/barback.dart';
@@ -27,9 +28,9 @@ import 'dart:isolate';
 import 'dart:convert';
 import 'dart:mirrors';
 
-import 'http://<<HOST_AND_PORT>>/packages/source_maps/span.dart';
-import 'http://<<HOST_AND_PORT>>/packages/stack_trace/stack_trace.dart';
-import 'http://<<HOST_AND_PORT>>/packages/barback/barback.dart';
+import '<<URL_BASE>>/packages/source_maps/span.dart';
+import '<<URL_BASE>>/packages/stack_trace/stack_trace.dart';
+import '<<URL_BASE>>/packages/barback/barback.dart';
 
 /// Sets up the initial communication with the host isolate.
 void main(_, SendPort replyTo) {
@@ -447,10 +448,10 @@ Future<Set> loadTransformers(BarbackServer server, BarbackMode mode,
   return id.getAssetId(server.barback).then((assetId) {
     var path = assetId.path.replaceFirst('lib/', '');
     // TODO(nweiz): load from a "package:" URI when issue 12474 is fixed.
-    var hostAndPort = '${server.address.address}:${server.port}';
-    var uri = 'http://$hostAndPort/packages/${id.package}/$path';
-    var code = 'import "$uri";' +
-        _TRANSFORMER_ISOLATE.replaceAll('<<HOST_AND_PORT>>', hostAndPort);
+    var baseUrl = baseUrlForAddress(server.address, server.port);
+    var uri = '$baseUrl/packages/${id.package}/$path';
+    var code = 'import "$uri";\n' +
+        _TRANSFORMER_ISOLATE.replaceAll('<<URL_BASE>>', baseUrl);
     log.fine("Loading transformers from $assetId");
 
     var port = new ReceivePort();