Turn strict mode off in the dartanalyzer

pkg/custom_element/lib/custom_element.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.
 
 /**
  * Custom Elements let authors define their own elements. Authors associate code
  * with custom tag names, and then use those custom tag names as they would any
  * standard tag. See <www.polymer-project.org/platform/custom-elements.html>
  * for more information.
  */
@@ skipping 68 matching lines @@
  * Initialize any registered custom elements recursively in the [node] tree.
  * For convenience this returns the [node] instance.
  *
  * *Warning*: this API is temporary until [dart:html] supports custom elements.
  */
 Node initCustomElements(Node node) {
   for (var c = node.firstChild; c != null; c = c.nextNode) {
     initCustomElements(c);
   }
   if (node is Element) {
-    var ctor = _customElements[node.localName];
+    var ctor = _customElements[(node as Element).localName];
     if (ctor == null) {
-      var attr = node.attributes['is'];
+      var attr = (node as Element).attributes['is'];
       if (attr != null) ctor = _customElements[attr];
     }
     if (ctor != null) _initCustomElement(node, ctor);
   }
   return node;
 }
 
 /**
  * The base class for all Dart web components. In addition to the [Element]
  * interface, it also provides lifecycle methods:
@@ skipping 557 matching lines @@
       for (var removed in record.removedNodes) {
         if (identical(node, removed)) {
           observer.disconnect();
           element.removed();
           return;
         }
       }
     }
   }).observe(element.parentNode, childList: true);
 }