Making all DOM types abstract and removing superfluous Dartium constructors.

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 $LIBRARYNAME;
 
-$(ANNOTATIONS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
+$(ANNOTATIONS)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
 $!MEMBERS
 
 $if DART2JS
   @DomName('Document.body')
   BodyElement body;
 $else
   @DomName('Document.body')
   BodyElement get body => $dom_body;
 
   @DomName('Document.body')
@@ skipping 146 matching lines @@
   @Experimental
   String get visibilityState => $dom_webkitVisibilityState;
 
 
 $if DART2JS
   @Creates('Null')  // Set from Dart code; does not instantiate a native type.
 $endif
   // Note: used to polyfill <template>
   Document _templateContentsOwner;
 }