Move noSuchMethod hook from UnknownElement to Element

lib/dom/templates/html/impl/impl_Element.darttemplate

 // 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.
 
 // TODO(jacobr): use _Lists.dart to remove some of the duplicated
 // functionality.
 class _ChildrenElementList implements ElementList {
   // Raw Element.
   final _ElementImpl _element;
   final _HTMLCollectionImpl _childElements;
@@ skipping 701 matching lines @@
   Future<CSSStyleDeclaration> get computedStyle() {
      // TODO(jacobr): last param should be null, see b/5045788
      return getComputedStyle('');
   }
 
   Future<CSSStyleDeclaration> getComputedStyle(String pseudoElement) {
     return _createMeasurementFuture(
         () => _window.$dom_getComputedStyle(this, pseudoElement),
         new Completer<CSSStyleDeclaration>());
   }
+
+  // Hooks to support custom WebComponents.
+  var xtag;
+
+$if DARTIUM
+  noSuchMethod(String name, List args) {
+    if (dynamicUnknownElementDispatcher == null) {
+      throw new NoSuchMethodException(this, name, args);
+    } else {
+      return dynamicUnknownElementDispatcher(this, name, args);
+    }
+  }
+$else
+  // TODO(vsm): Implement noSuchMethod or similar for dart2js.
+$endif
+
 $!MEMBERS
 }
 
+// Temporary dispatch hook to support WebComponents.
+Function dynamicUnknownElementDispatcher;
+
 final _START_TAG_REGEXP = const RegExp('<(\\w+)');
 class _ElementFactoryProvider {
   static final _CUSTOM_PARENT_TAG_MAP = const {
     'body' : 'html',
     'head' : 'html',
     'caption' : 'table',
     'td': 'tr',
     'colgroup': 'table',
     'col' : 'colgroup',
     'tr' : 'tbody',
@@ skipping 41 matching lines @@
 
   /** @domName Document.createElement */
 $if DART2JS
   // Optimization to improve performance until the dart2js compiler inlines this
   // method.
   factory Element.tag(String tag) native "return document.createElement(tag)";
 $else
   factory Element.tag(String tag) => _document.$dom_createElement(tag);
 $endif
 }