Refactor handling of source map information.

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

 // Copyright (c) 2012, 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 dart2js.code_output;
 
 import 'dart:async';
 
-import 'source_map_builder.dart';
+import 'source_information.dart';
 
 class CodeOutputMarker {
   final int offsetDelta;
   final SourceFileLocation sourcePosition;
 
   CodeOutputMarker(this.offsetDelta, this.sourcePosition);
 }
 
 abstract class CodeOutputListener {
   void onText(String text);
@@ skipping 135 matching lines @@
   }
 
   void close() {
     output.close();
     super.close();
     if (_listeners != null) {
       _listeners.forEach((listener) => listener.onDone(length));
     }
   }
 }