fix Polymer to work with latest JS interop

pkg/pkg.status

 # 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.
 
 # Don't run any test-like files that show up in packages directories. It
 # shouldn't be necessary to run "pub install" in these packages, but if you do
 # it shouldn't break the tests.
 */packages/*/*: Skip
 */*/packages/*/*: Skip
 */*/*/packages/*/*: Skip
 */*/*/*/packages/*/*: Skip
 
 # Skip non-test files ending with "_test".
 scheduled_test/lib/*: Skip
 polymer/example/scoped_style/*: Skip
-polymer/test/instance_attrs_test: Pass, Slow, Fail # Issue 14248
 
 scheduled_test/test/scheduled_server_test: Pass, Slow, Fail # Issue 9231, 13524
 scheduled_test/test/scheduled_process_test: Pass, Slow # Issue 9231
 
 
 # Skip test not runnable via test.dart
 third_party/html5lib/test/dom_compat_test: Skip
 third_party/html5lib/test/browser/browser_test: Skip
 
 [ $compiler == dart2js ]
@@ skipping 269 matching lines @@
 # pkg issue 13944; Missing inherited members: 'ListChangeRecord.addedCount' and 'ListChangeRecord.removedCount'
 custom_element/test/analyzer_test: fail
 mdv/test/analyzer_test: fail
 observe/test/observe_test: fail
 
 # pkg issue 13945; Missing inherited member 'Trace.frames'
 observe/test/observe_test: fail
 
 [ $compiler == none && ( $runtime == dartium || $runtime == drt ) ]
 polymer/test/prop_attr_reflection_test: fail # Issue 14036