Use common.dart to re-export commonly used entities.

pkg/compiler/lib/src/io/start_end_information.dart

 // Copyright (c) 2015, 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.
 
 /// Source information system that maps spans of Dart AST nodes to spans of
 /// JavaScript nodes.
 
 library dart2js.source_information.start_end;
 
+import '../common.dart';
 import '../diagnostics/messages.dart' show
-    MessageKind,
     MessageTemplate;
-import '../diagnostics/source_span.dart' show
-    SourceSpan;
 import '../elements/elements.dart' show
     AstElement,
     LocalElement;
 import '../js/js.dart' as js;
 import '../js/js_source_mapping.dart';
 import '../tokens/token.dart' show Token;
 import '../tree/tree.dart' show Node, Send;
 
 import 'source_file.dart';
 import 'source_information.dart';
@@ skipping 202 matching lines @@
 
   @override
   SourceInformationBuilder forContext(
       AstElement element, {SourceInformation sourceInformation}) {
     return new StartEndSourceInformationBuilder(element);
   }
 }