stacktrace

Exception: Bad state: No element
Uncaught SyntaxError: Failed to execute 'querySelector' on 'Element': '#packages/test/menu' is not a valid selector. (http://127.0.0.1:8080/index.html:1558)
Exception caught during observer callback: Error: Failed to execute 'querySelector' on 'Element': '#packages/test/menu' is not a valid selector.
    at Error (native)
    at core-iconset-svg.Polymer.iconById (http://127.0.0.1:8080/index.html:1558:59)
    at core-iconset-svg.Polymer.cloneIcon (http://127.0.0.1:8080/index.html:1562:25)
    at core-iconset-svg.Polymer.applyIcon (http://127.0.0.1:8080/index.html:1606:24)
    at core-icon.Polymer.updateIcon (http://127.0.0.1:8080/index.html:1510:17)
    at core-icon.g.invokeMethod (http://127.0.0.1:8080/packages/polymer/src/js/polymer/polymer.js:12:13320)
    at core-icon.g.notifyPropertyChanges (http://127.0.0.1:8080/packages/polymer/src/js/polymer/polymer.js:12:11606)
    at Object.Observer.report_ (http://127.0.0.1:8080/packages/web_components/platform.js:12:12616)
    at Object.createObject.check_ (http://127.0.0.1:8080/packages/web_components/platform.js:12:18105)
    at c (http://127.0.0.1:8080/packages/web_components/platform.js:12:5467) (http://127.0.0.1:8080/packages/web_components/platform.js:12)

test.dart

import 'package:polymer/polymer.dart';

@CustomTag('test-app')
class TestApp extends PolymerElement {
  TestApp.created() : super.created();
}

test.html

<link rel="import" href="../../packages/core_elements/core_header_panel.html">
<link rel="import" href="../../packages/core_elements/core_toolbar.html">
<link rel="import" href="../../packages/core_elements/core_menu.html">
<link rel="import" href="../../packages/core_elements/core_menu_button.html">

<polymer-element name="test-app">
  <template>
    <core-header-panel fit>
      <core-toolbar>
        <core-menu-button icon="menu" label="menu">
          <core-menu-item>
          </core-menu-item>
        </core-menu-button>
        <div core-flex>Test</div>
      </core-toolbar>
      <p>Hello from inside a custom element!</p>
    </core-header-panel>
  </template>
  <script src="test_app.dart" type="application/dart"></script>
</polymer-element>