Cleanup of various DOM dart2js and dart_analyzer warnings

tools/dom/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 $LIBRARYNAME;
 
 class _ChildrenElementList extends ListBase<Element> {
   // Raw Element.
   final Element _element;
   final HtmlCollection _childElements;
@@ skipping 618 matching lines @@
     } else if (JS('bool', '!!#.mozMatchesSelector', this)) {
       return JS('bool', '#.mozMatchesSelector(#)', this, selectors);
     } else if (JS('bool', '!!#.msMatchesSelector', this)) {
       return JS('bool', '#.msMatchesSelector(#)', this, selectors);
     }
     throw new UnsupportedError("Not supported on this platform");
   }
 $else
 $endif
 
-  @Creates('Null')
+$if DART2JS
+  @Creates('Null') // Set from Dart code; does not instantiate a native type.
+$endif
   Map<String, StreamSubscription> _attributeBindings;
 
   // TODO(jmesserly): I'm concerned about adding these to every element.
   // Conceptually all of these belong on TemplateElement. They are here to
   // support browsers that don't have <template> yet.
   // However even in the polyfill they're restricted to certain tags
   // (see [isTemplate]). So we can probably convert it to a (public) mixin, and
   // only mix it in to the elements that need it.
 $if DART2JS
   @Creates('Null')  // Set from Dart code; does not instantiate a native type.
@@ skipping 384 matching lines @@
   const ScrollAlignment._internal(this._value);
   toString() => 'ScrollAlignment.$_value';
 
   /// Attempt to align the element to the top of the scrollable area.
   static const TOP = const ScrollAlignment._internal('TOP');
   /// Attempt to center the element in the scrollable area.
   static const CENTER = const ScrollAlignment._internal('CENTER');
   /// Attempt to align the element to the bottom of the scrollable area.
   static const BOTTOM = const ScrollAlignment._internal('BOTTOM');
 }