Adding Element.created constructor

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 DOM elements.
  *
  * This library provides access to the Polymer project's
  * [Custom Elements]
  * (http://www.polymer-project.org/platform/custom-elements.html)
@@ skipping 153 matching lines @@
     return root;
   }
 
   getShadowRoot(String componentName) => _generatedRoots[componentName];
 
   /**
    * Invoked when this component gets created.
    * Note that [root] will be a [ShadowRoot] if the browser supports Shadow DOM.
    */
   void created() {}
+  // Added for analyzer warnings
+  @deprecated
+  void createdCallback() {}
 
   /** Invoked when this component gets inserted in the DOM tree. */
   void inserted() {}
   @deprecated
   void enteredView() {}
 
   /** Invoked when this component is removed from the DOM tree. */
   void removed() {}
   @deprecated
   void leftView() {}
@@ skipping 459 matching lines @@
       for (var removed in record.removedNodes) {
         if (identical(node, removed)) {
           observer.disconnect();
           element.removed();
           return;
         }
       }
     }
   }).observe(element.parentNode, childList: true);
 }