Strip unused functionality from dart:html and fix strong mode errors. Switch from blacklisting pure…

tools/dom/templates/html/impl/impl_Window.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;
 
 @DocsEditable()
 $if DART2JS
 $(ANNOTATIONS)@Native("Window,DOMWindow")
 $(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS {
@@ skipping 321 matching lines @@
 }
 $endif
 
 class _BeforeUnloadEventStreamProvider implements
     EventStreamProvider<BeforeUnloadEvent> {
   final String _eventType;
 
   const _BeforeUnloadEventStreamProvider(this._eventType);
 
   Stream<BeforeUnloadEvent> forTarget(EventTarget e, {bool useCapture: false}) {
-    var stream = new _EventStream(e, _eventType, useCapture);
 $if DART2JS
+    // Specify the generic type for EventStream only in dart2js to avoid
+    // checked mode errors in dartium.
+    var stream = new _EventStream<BeforeUnloadEvent>(e, _eventType, useCapture);
     var controller = new StreamController<BeforeUnloadEvent>(sync: true);
 
     stream.listen((event) {
       var wrapped = new _BeforeUnloadEvent(event);
       controller.add(wrapped);
     });
 
     return controller.stream;
 $else
+    var stream = new _EventStream(e, _eventType, useCapture);
     return stream;
 $endif
   }
 
   String getEventType(EventTarget target) {
     return _eventType;
   }
 
   ElementStream<BeforeUnloadEvent> forElement(Element e, {bool useCapture: false}) {
+$if DART2JS
+    // Specify the generic type for _ElementEventStreamImpl only in dart2js to
+    // avoid checked mode errors in dartium.
+    return new _ElementEventStreamImpl<BeforeUnloadEvent>(e, _eventType, useCapture);
+$else
     return new _ElementEventStreamImpl(e, _eventType, useCapture);
+$endif
   }
 
   ElementStream<BeforeUnloadEvent> _forElementList(ElementList e,
       {bool useCapture: false}) {
+$if DART2JS
+    // Specify the generic type for _ElementEventStreamImpl only in dart2js to
+    // avoid checked mode errors in dartium.
+    return new _ElementListEventStreamImpl<BeforeUnloadEvent>(e, _eventType, useCapture);
+$else
     return new _ElementListEventStreamImpl(e, _eventType, useCapture);
+$endif
   }
 }