Removing unnecessary warning when parsing Json.

pkg/source_maps/lib/parser.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 the top-level function to parse source maps version 3.
 library source_maps.parser;
 
 import 'dart:collection';
 import 'dart:convert';
 
@@ skipping 13 matching lines @@
   parseJson(JSON.decode(jsonMap), otherMaps: otherMaps);
 
 /// Parses a source map directly from a json map object.
 Mapping parseJson(Map map, {Map<String, Map> otherMaps}) {
   if (map['version'] != 3) {
     throw new ArgumentError(
         'unexpected source map version: ${map["version"]}. '
         'Only version 3 is supported.');
   }
 
-  if (!map.containsKey('file')) {

[Siggi Cherem (dart-lang), 2014/12/04 00:12:23]

oh cool - it seems they made it optional about a year ago (this code was
probably written before then).

-    print('warning: missing "file" entry in source map');
-  }
-
   if (map.containsKey('sections')) {
     if (map.containsKey('mappings') || map.containsKey('sources') ||
         map.containsKey('names')) {
       throw new FormatException('map containing "sections" '
           'cannot contain "mappings", "sources", or "names".');
     }
     return new MultiSectionMapping.fromJson(map['sections'], otherMaps);
   }
   return new SingleMapping.fromJson(map);
 }
@@ skipping 461 matching lines @@
   static const _TokenKind EOF = const _TokenKind(isEof: true);
   static const _TokenKind VALUE = const _TokenKind();
   final bool isNewLine;
   final bool isNewSegment;
   final bool isEof;
   bool get isValue => !isNewLine && !isNewSegment && !isEof;
 
   const _TokenKind(
       {this.isNewLine: false, this.isNewSegment: false, this.isEof: false});
 }