fix polymer copy-instance-attributes feature

pkg/polymer/test/instance_attrs_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.
+
+import 'dart:html';
+import 'package:unittest/unittest.dart';
+import 'package:unittest/html_config.dart';
+import 'package:polymer/polymer.dart';
+
+main() {
+  useHtmlConfiguration();
+
+  test('attributes were deserialized', () {
+    var elem = query('my-element').xtag;
+
+    expect(elem.attributes, {'foo': '123', 'bar': 'hi', 'baz': 'world'},
+        reason: 'attributes should be copied to instance');
+
+    var text = elem.shadowRoot.text;
+    // Collapse adjacent whitespace like a browser would:
+    text = text.replaceAll('\n', ' ').replaceAll(new RegExp(r'\s+'), ' ');
+
+    expect(text, " foo: 123 bar: hi baz: world ",
+        reason: 'text should match expected HTML template');
+  });
+}