Add annotations on native fields and methods

sdk/lib/html/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.
 
 part of html;
 
 // TODO(jacobr): use _Lists.dart to remove some of the duplicated
 // functionality.
 class _ChildrenElementList implements List {
   // Raw Element.
@@ skipping 599 matching lines @@
   /**
    * Experimental support for [web components][wc]. This field stores a
    * reference to the component implementation. It was inspired by Mozilla's
    * [x-tags][] project. Please note: in the future it may be possible to
    * `extend Element` from your class, in which case this field will be
    * deprecated and will simply return this [Element] object.
    *
    * [wc]: http://dvcs.w3.org/hg/webcomponents/raw-file/tip/explainer/index.html
    * [x-tags]: http://x-tags.org/
    */
+$if DART2JS
+  @Creates('Null')  // Set from Dart code; does not instantiate a native type.

[ngeoffray, 2012/11/20 08:50:13]

Why do you need this one?

[sra1, 2012/11/20 09:01:42]

xtag is really a Dart-only field used by the WebComponents compiler.

The default (safe) assumption is that accessing a native field will create any
native class that is a subtype of the field's declared type.

This field is always assigned from Dart code so there is no path hidden in the
browser that might create an instance x that satisfies "x is T" where T is the
declared type.

@Create('Null') is a way of expressing this without inventing a new annotations.

+$endif
   var xtag;
 
 $if DARTIUM
   noSuchMethod(InvocationMirror invocation) {
     if (dynamicUnknownElementDispatcher == null) {
       throw new NoSuchMethodError(this, invocation.memberName,
                                         invocation.positionalArguments,
                                         invocation.namedArguments);
     } else {
       String hackedName = invocation.memberName;
@@ skipping 130 matching lines @@
 $if DART2JS
   // Optimization to improve performance until the dart2js compiler inlines this
   // method.
   static Element createElement_tag(String tag) =>
       JS('Element', 'document.createElement(#)', tag);
 $else
   static Element createElement_tag(String tag) =>
       document.$dom_createElement(tag);
 $endif
 }