Move a number of packages and some of pub over to using source_span.

sdk/lib/_internal/pub/lib/src/barback/transformer_isolate.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.transformer_isolate;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:isolate';
 
 import 'package:barback/barback.dart';
-import 'package:source_maps/source_maps.dart';
+import 'package:source_span/source_span.dart';
 import 'package:stack_trace/stack_trace.dart';
 
 import '../../../asset/dart/serialize.dart';
 import '../barback.dart';
 import '../exceptions.dart';
 import '../dart.dart' as dart;
 import '../log.dart' as log;
 import '../utils.dart';
 import 'asset_environment.dart';
 import 'barback_server.dart';
@@ skipping 92 matching lines @@
           .toSet();
       log.fine("Transformers from $config: $transformers");
       return transformers;
     }).catchError((error, stackTrace) {
       throw new TransformerLoadError(error, config.span);
     });
   }
 }
 
 /// An error thrown when a transformer fails to load.
-class TransformerLoadError extends SpanException implements WrappedException {
+class TransformerLoadError extends SourceSpanException
+    implements WrappedException {
   final CrossIsolateException innerError;
   Chain get innerChain => innerError.stackTrace;
 
-  TransformerLoadError(CrossIsolateException error, Span span)
+  TransformerLoadError(CrossIsolateException error, SourceSpan span)
       : innerError = error,
         super("Error loading transformer: ${error.message}", span);
 }