Add CodeOutput to prepare for emission without in-memory buffers.

pkg/compiler/lib/src/io/source_map_builder.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 source_map_builder;
+library dart2js.source_map_builder;
 
-import 'util/util.dart';
-import 'scanner/scannerlib.dart' show Token;
-import 'source_file.dart';
-import 'util/uri_extras.dart' show relativize;
+import '../util/util.dart';
+import '../scanner/scannerlib.dart' show Token;
+import '../source_file.dart';
+import '../util/uri_extras.dart' show relativize;
 
 class SourceMapBuilder {
   static const int VLQ_BASE_SHIFT = 5;
   static const int VLQ_BASE_MASK = (1 << 5) - 1;
   static const int VLQ_CONTINUATION_BIT = 1 << 5;
   static const int VLQ_CONTINUATION_MASK = 1 << 5;
   static const String BASE64_DIGITS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmn'
                                       'opqrstuvwxyz0123456789+/';
 
   final Uri uri;
@@ skipping 237 matching lines @@
 
   TokenSourceFileLocation(SourceFile sourceFile, this.token, this.name)
     : super(sourceFile);
 
   int get offset => token.charOffset;
 
   String getSourceName() {
     return name;
   }
 }