Allowing Window.onBeforeUnload event to work properly.

sdk/lib/_internal/compiler/implementation/lib/native_helper.dart

 // 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 _js_helper;
 
 String typeNameInChrome(obj) {
   String name = JS('String', "#.constructor.name", obj);
   return typeNameInWebKitCommon(name);
 }
@@ skipping 23 matching lines @@
 String typeNameInOpera(obj) {
   String name = JS('String', '#', constructorNameFallback(obj));
   if (name == 'Window') return 'DOMWindow';
   if (name == 'ApplicationCache') return 'DOMApplicationCache';
   return name;
 }
 
 String typeNameInFirefox(obj) {
   String name = JS('String', '#', constructorNameFallback(obj));
   if (name == 'Window') return 'DOMWindow';
+  if (name == 'BeforeUnloadEvent') return 'Event';
   if (name == 'CSS2Properties') return 'CSSStyleDeclaration';
   if (name == 'DataTransfer') return 'Clipboard';
   if (name == 'DragEvent') return 'MouseEvent';
   if (name == 'GeoGeolocation') return 'Geolocation';
   if (name == 'MouseScrollEvent') return 'WheelEvent';
   if (name == 'OfflineResourceList') return 'DOMApplicationCache';
   if (name == 'WorkerMessageEvent') return 'MessageEvent';
   if (name == 'XMLDocument') return 'Document';
   return name;
 }
 
 String typeNameInIE(obj) {
   String name = JS('String', '#', constructorNameFallback(obj));
   if (name == 'Window') return 'DOMWindow';
   if (name == 'Document') {
     // IE calls both HTML and XML documents 'Document', so we check for the
     // xmlVersion property, which is the empty string on HTML documents.
     if (JS('bool', '!!#.xmlVersion', obj)) return 'Document';
     return 'HTMLDocument';
   }
   if (name == 'ApplicationCache') return 'DOMApplicationCache';
+  if (name == 'BeforeUnloadEvent') return 'Event';
   if (name == 'CanvasPixelArray') return 'Uint8ClampedArray';
   if (name == 'DataTransfer') return 'Clipboard';
   if (name == 'DragEvent') return 'MouseEvent';
   if (name == 'HTMLDDElement') return 'HTMLElement';
   if (name == 'HTMLDTElement') return 'HTMLElement';
   if (name == 'HTMLTableDataCellElement') return 'HTMLTableCellElement';
   if (name == 'HTMLTableHeaderCellElement') return 'HTMLTableCellElement';
   if (name == 'HTMLPhraseElement') return 'HTMLElement';
   if (name == 'MSStyleCSSProperties') return 'CSSStyleDeclaration';
   if (name == 'MouseWheelEvent') return 'WheelEvent';
@@ skipping 347 matching lines @@
   }
   return result;
 }
 
 /**
  * Called by the compiler to setup [_dynamicMetadata].
  */
 void dynamicSetMetadata(List<List<String>> inputTable) {
   _dynamicMetadata = buildDynamicMetadata(inputTable);
 }