Revert "Fix a few strong mode errors in dart:html"

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;
 
 $(ANNOTATIONS)$(NATIVESPEC)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS {
 $!MEMBERS
@@ skipping 134 matching lines @@
    *   API](http://docs.webplatform.org/wiki/tutorials/using_the_full-screen_api)
    *   from WebPlatform.org.
    * * [Fullscreen specification](http://www.w3.org/TR/fullscreen/) from W3C.
    */
   @DomName('Document.webkitFullscreenElement')
   @SupportedBrowser(SupportedBrowser.CHROME)
   @SupportedBrowser(SupportedBrowser.SAFARI)
   @Experimental()
   Element get fullscreenElement => _webkitFullscreenElement;
 
+  /**
+   * Returns true if this document can display elements in fullscreen mode.
+   *
+   * ## Other resources
+   *
+   * * [Using the fullscreen
+   *   API](http://docs.webplatform.org/wiki/tutorials/using_the_full-screen_api)
+   *   from WebPlatform.org.
+   * * [Fullscreen specification](http://www.w3.org/TR/fullscreen/) from W3C.
+   */
+  @DomName('Document.webkitFullscreenEnabled')
+  @SupportedBrowser(SupportedBrowser.CHROME)
+  @SupportedBrowser(SupportedBrowser.SAFARI)
+  @Experimental()
+  bool get fullscreenEnabled => _webkitFullscreenEnabled;
+
   @DomName('Document.webkitHidden')
   @SupportedBrowser(SupportedBrowser.CHROME)
   @SupportedBrowser(SupportedBrowser.SAFARI)
   @Experimental()
   bool get hidden => _webkitHidden;
 
   @DomName('Document.visibilityState')
   @SupportedBrowser(SupportedBrowser.CHROME)
   @SupportedBrowser(SupportedBrowser.FIREFOX)
   @SupportedBrowser(SupportedBrowser.IE, '10')
@@ skipping 344 matching lines @@
   /// parameter must be provided.
   @Experimental()
   ElementUpgrader createElementUpgrader(Type type, {String extendsTag}) {
 $if DART2JS
     return new _JSElementUpgrader(this, type, extendsTag);
 $else
     return new _VMElementUpgrader(this, type, extendsTag);
 $endif
   }
 }