Only support the new source_span spans in barback.

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

 // Copyright (c) 2014, 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.barback.asset_environment;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:barback/barback.dart';
@@ skipping 655 matching lines @@
   // If the relevant asset isn't the primary input, mention it unless the
   // message already does.
   if (entry.assetId != entry.transform.primaryId &&
       !messageMentionsAsset(entry.assetId)) {
     prefixParts.add("with input ${entry.assetId}");
   }
 
   var prefix = "[${prefixParts.join(' ')}]:";
   var message = entry.message;
   if (entry.span != null) {
-    message = entry.span.getLocationMessage(entry.message);
+    message = entry.span.message(entry.message);
   }
 
   switch (entry.level) {
     case LogLevel.ERROR:
       log.error("${log.red(prefix)}\n$message");
       break;
 
     case LogLevel.WARNING:
       log.warning("${log.yellow(prefix)}\n$message");
       break;
@@ skipping 54 matching lines @@
   String toString() => "polling";
 }
 
 class _NoneWatcherType implements WatcherType {
   const _NoneWatcherType();
 
   DirectoryWatcher create(String directory) => null;
 
   String toString() => "none";
 }