Alphabetize json output.

tools/html_json_doc/lib/html_to_json.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 for extracting the documentation comments from files generated by
  * the HTML library. The comments are stored in a JSON file.
  *
  * Comments must be in either the block style with leading *s:
  *
@@ skipping 281 matching lines @@
   var output;
 
   if (json is List) {
     var recursiveOutput =
         Strings.join(json.map((e) => 
             prettyPrintJson(e, '$indentation  ')), ',\n');
     output = '$indentation[\n'
       '$recursiveOutput'
       '\n$indentation]';
   } else if (json is Map) {
+    var keys = json.keys
+      ..sort();
+
     // TODO(amouravski): No newline after :
-    var mapList = json.keys.map((key) =>
+    var mapList = keys.map((key) =>
         '$indentation${JSON.stringify(key)}:\n'
         '${prettyPrintJson(json[key], '$indentation  ')}');
     var recursiveOutput = Strings.join(mapList, ',\n');
     output = '$indentation{\n'
       '$recursiveOutput'
       '\n$indentation}';
   } else {
     output = '$indentation${JSON.stringify(json)}';
   }
   return output;
-}
+}