Add custom annotations to some APIs for native tree shaking.

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

Index: sdk/lib/html/templates/html/impl/impl_DocumentFragment.darttemplate
diff --git a/sdk/lib/html/templates/html/impl/impl_DocumentFragment.darttemplate b/sdk/lib/html/templates/html/impl/impl_DocumentFragment.darttemplate
index c32a8fb6efd26106d4be18dff2a84d65c6cb327d..c636745d0f08a1c5c5f51acea101b772128d040a 100644
--- a/sdk/lib/html/templates/html/impl/impl_DocumentFragment.darttemplate
+++ b/sdk/lib/html/templates/html/impl/impl_DocumentFragment.darttemplate
@@ -28,6 +28,11 @@ class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
   factory $CLASSNAME.svg(String svgContent) =>
       new _$(CLASSNAME)FactoryProvider.createDocumentFragment_svg(svgContent);
 
+$if DART2JS
+  // This is a field of a native object, but used only from Dart code, so does
+  // not instantiate any native classes.
+  @Creates('Null')

[blois, 2012/11/19 20:46:48]

Why is @Creates('Null') not the default behavior?

[sra1, 2012/11/19 23:15:07]

The default behaviour is @Creates(the-return/field-type)

Otherwise all fields and all methods need annotating.

+$endif
   List<Element> _elements;
 
   List<Element> get elements {