Bring back initPolymer, allow boot.js only if using "polymer_experimental.html".

pkg/polymer/example/canonicalization3/test/bad_lib_import_negative_test.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.
-
-/// Tests how canonicalization works when using the deployed app.
-library canonicalization.bad_lib_import_negative;
-
-import 'package:unittest/unittest.dart';
-import 'package:unittest/html_config.dart';
-import 'package:polymer/polymer.dart';
-
-import 'package:canonicalization3/a.dart';
-import 'packages/canonicalization3/b.dart';
-import 'package:canonicalization3/c.dart';
-import 'package:canonicalization3/d.dart' as d1;
-import 'packages/canonicalization3/d.dart' as d2;
-
-@initMethod
-main() {
-  useHtmlConfiguration();
-
-  setUp(() => Polymer.onReady);
-
-  test('canonicalization', () {
-    // "package:" urls work the same during development and deployment
-    expect(a, 1, reason:
-      'deploy picks the "package:" url as the canonical url for script tags.');
-
-    // relative urls do not. true, we shouldn't be using 'packages/' above, so
-    // that's ok.
-    expect(b, 0, reason:
-      'deploy picks the "package:" url as the canonical url for script tags.');
-    expect(c, 2, reason: 'c was always imported with "package:" urls.');
-    expect(d1.d, 2, reason: 'both a and b are loaded using package: urls');
-
-    // same here
-    expect(d2.d, 0, reason: 'both a and b are loaded using package: urls');
-  });
-}