Add annotations on native fields and methods

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

Index: sdk/lib/html/templates/html/impl/impl_Element.darttemplate
diff --git a/sdk/lib/html/templates/html/impl/impl_Element.darttemplate b/sdk/lib/html/templates/html/impl/impl_Element.darttemplate
index d475ddfc6e313c3ca491175cb02f49070014e9e9..bf6e19acee42691eec21d45161133b3202d1a13f 100644
--- a/sdk/lib/html/templates/html/impl/impl_Element.darttemplate
+++ b/sdk/lib/html/templates/html/impl/impl_Element.darttemplate
@@ -617,6 +617,9 @@ abstract class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
    * [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