Adding a mechanism to 'upgrade' the Dart type of elements

tools/dom/src/dart2js_CustomElementSupport.dart

Index: tools/dom/src/dart2js_CustomElementSupport.dart
diff --git a/tools/dom/src/dart2js_CustomElementSupport.dart b/tools/dom/src/dart2js_CustomElementSupport.dart
index aa1c0372869484cefaff498db97b696d000ed05d..009f85767202a6d77e6f0b9f56a796483fecd84f 100644
--- a/tools/dom/src/dart2js_CustomElementSupport.dart
+++ b/tools/dom/src/dart2js_CustomElementSupport.dart
@@ -87,7 +87,7 @@ void _registerCustomElement(context, document, String tag, Type type,
   if (extendsTagName == null) {
     if (baseClassName != 'HTMLElement') {
       throw new UnsupportedError('Class must provide extendsTag if base '
-          'native class is not HTMLElement');
+          'native class is not HtmlElement');
     }
   } else {
     if (!JS('bool', '(#.createElement(#) instanceof window[#])',
@@ -128,3 +128,60 @@ void _registerCustomElement(context, document, String tag, Type type,
 void _initializeCustomElement(Element e) {
   // TODO(blois): Add validation that this is only in response to an upgrade.
 }
+
+/// Dart2JS implementation of ElementUpgrader
+class _JSElementUpgrader implements ElementUpgrader {
+  var _interceptor;
+  var _constructor;
+  var _nativeType;
+
+  _JSElementUpgrader(Document document, Type type, String extendsTag) {
+    var interceptorClass = findInterceptorConstructorForType(type);
+    if (interceptorClass == null) {
+      throw new ArgumentError(type);
+    }
+
+    _constructor = findConstructorForNativeSubclassType(type, 'created');
+    if (_constructor == null) {
+      throw new ArgumentError("$type has no constructor called 'created'");
+    }
+
+    // Workaround for 13190- use an article element to ensure that HTMLElement's
+    // interceptor is resolved correctly.
+    getNativeInterceptor(new Element.tag('article'));
+
+    var baseClassName = findDispatchTagForInterceptorClass(interceptorClass);
+    if (baseClassName == null) {
+      throw new ArgumentError(type);
+    }
+
+    if (extendsTag == null) {
+      if (baseClassName != 'HTMLElement') {
+        throw new UnsupportedError('Class must provide extendsTag if base '
+            'native class is not HtmlElement');
+      }
+      _nativeType = HtmlElement;
+    } else {
+      var element = document.createElement(extendsTag);
+      if (!JS('bool', '(# instanceof window[#])',
+          element, baseClassName)) {
+        throw new UnsupportedError(
+            'extendsTag does not match base native class');
+      }
+      _nativeType = element.runtimeType;
+    }
+
+    _interceptor = JS('=Object', '#.prototype', interceptorClass);
+  }
+
+  Element upgrade(Element element) {
+    // Only exact type matches are supported- cannot be a subclass.
+    if (element.runtimeType != _nativeType) {
+      throw new ArgumentError('element is not subclass of $_nativeType');
+    }
+
+    setNativeSubclassDispatchRecord(element, _interceptor);
+    JS('', '#(#)', _constructor, element);
+    return element;
+  }
+}