Changed how Experimental annotation works. No longer is a constructor.

tools/dom/templates/html/impl/impl_HTMLDocument.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.
 
 // WARNING: Do not edit - generated code.
 
 part of html;
 
 $(ANNOTATIONS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
 $!MEMBERS
@@ skipping 45 matching lines @@
    *     context.fillStyle = 'red';
    *     context.fillRect(0, 0, 100, 100);
    *
    * See also:
    *
    * * [supportsCssCanvasContext]
    * * [CanvasElement.getContext]
    */
   @SupportedBrowser(SupportedBrowser.CHROME)
   @SupportedBrowser(SupportedBrowser.SAFARI)
-  @Experimental()
+  @Experimental
   @DomName('Document.getCSSCanvasContext')
   CanvasRenderingContext getCssCanvasContext(String contextId, String name,
       int width, int height) {
     return document.$dom_getCssCanvasContext(contextId, name, width, height);
   }
 
   @DomName('Document.head')
   HeadElement get head => document.$dom_head;
 
   @DomName('Document.lastModified')
@@ skipping 49 matching lines @@
   @DomName('Document.webkitIsFullScreen')
   bool get webkitIsFullScreen => document.$dom_webkitIsFullScreen;
 
   @DomName('Document.webkitPointerLockElement')
   Element get webkitPointerLockElement =>
       document.$dom_webkitPointerLockElement;
 
   @DomName('Document.webkitVisibilityState')
   String get webkitVisibilityState => document.$dom_webkitVisibilityState;
 }