Fixes from polymer.dart API review

pkg/polymer/lib/polymer.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.
 
 /**
  * Custom HTML tags, data binding, and templates for building
  * structured, encapsulated, client-side web apps.
  *
  * Polymer.dart, the next evolution of Web UI,
  * is an in-progress Dart port of the
@@ skipping 42 matching lines @@
 import 'package:logging/logging.dart' show Logger, Level;
 import 'package:meta/meta.dart' show deprecated;
 import 'package:observe/observe.dart';
 import 'package:observe/src/dirty_check.dart' show dirtyCheckZone;
 import 'package:path/path.dart' as path;
 import 'package:polymer_expressions/polymer_expressions.dart'
     show PolymerExpressions;
 import 'package:template_binding/template_binding.dart';
 
 import 'deserialize.dart' as deserialize;
-import 'job.dart';
-import 'platform.dart' as platform;
 import 'src/reflected_type.dart';
 
 export 'package:observe/observe.dart';
 export 'package:observe/html.dart';
 
 part 'src/boot.dart';
 part 'src/declaration.dart';
 part 'src/instance.dart';
+part 'src/job.dart';
 part 'src/loader.dart';