Update charted to 0.4.8 and roll

packages/source_maps/lib/builder.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.
 
 /// Contains a builder object useful for creating source maps programatically.
 library source_maps.builder;
 
 // TODO(sigmund): add a builder for multi-section mappings.
 
 import 'dart:convert';
@@ skipping 42 matching lines @@
   /// Encodes all mappings added to this builder as a json map.
   Map build(String fileUrl) {
     return new SingleMapping.fromEntries(this._entries, fileUrl).toJson();
   }
 
   /// Encodes all mappings added to this builder as a json string.
   String toJson(String fileUrl) => JSON.encode(build(fileUrl));
 }
 
 /// An entry in the source map builder.
-class Entry implements Comparable {
+class Entry implements Comparable<Entry> {
   /// Span denoting the original location in the input source file
   final SourceLocation source;
 
   /// Span indicating the corresponding location in the target file.
   final SourceLocation target;
 
   /// An identifier name, when this location is the start of an identifier.
   final String identifierName;
 
   /// Creates a new [Entry] mapping [target] to [source].
   Entry(this.source, this.target, this.identifierName);
 
   /// Implements [Comparable] to ensure that entries are ordered by their
   /// location in the target file. We sort primarily by the target offset
   /// because source map files are encoded by printing each mapping in order as
   /// they appear in the target file.
   int compareTo(Entry other) {
     int res = target.compareTo(other.target);
     if (res != 0) return res;
     res = source.sourceUrl.toString().compareTo(
         other.source.sourceUrl.toString());
     if (res != 0) return res;
     return source.compareTo(other.source);
   }
 }