Fixed few more issues with upgrader and custom event identitiy

tools/dom/templates/html/impl/impl_CustomEvent.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 {
   $if DART2JS
@@ skipping 16 matching lines @@
         detail = convertDartToNative_SerializedScriptValue(detail);
 $endif
         e._initCustomEvent(type, canBubble, cancelable, detail);
       } catch(_) {
         e._initCustomEvent(type, canBubble, cancelable, null);
       }
     } else {
       e._initCustomEvent(type, canBubble, cancelable, null);
     }
 
+$if DARTIUM
+    // Need for identity.
+    e.blink_jsObject['dart_class'] = e;
+
+$endif
     return e;
   }
 
   @DomName('CustomEvent.detail')
   get detail {
     if (_dartDetail != null) {
       return _dartDetail;
     }
     return _detail;
   }
 $!MEMBERS
 }