Add linter by default for polymer's pub-build, also cleans up the linter code.

pkg/polymer/lib/src/build/script_compactor.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.
 
 /** Transfomer that combines multiple dart script tags into a single one. */
 library polymer.src.build.script_compactor;
 
 import 'dart:async';
 import 'dart:convert';
 
@@ skipping 86 matching lines @@
             ..writeln('    ]);')
             ..writeln('  i${i - 1}.main();')
             ..writeln('}');
 
         transform.addOutput(new Asset.fromString(
               bootstrapId, buffer.toString()));
         transform.addOutput(new Asset.fromString(id, document.outerHtml));
       });
     });
   }
+
+  String toString() => 'polymer-script-compactor';
 }
 
 const MAIN_HEADER = """
 library app_bootstrap;
 
 import 'package:polymer/polymer.dart';
 """;