Limit beforeunload returnValue propagation to event handlers.

Source/bindings/v8/V8AbstractEventListener.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 131 matching lines @@
         else
             setHiddenValue(v8Context->GetIsolate(), v8Context->Global(), eventSymbol, savedEvent);
         tryCatch.Reset();
     }
 
     ASSERT(!handleOutOfMemory() || returnValue.IsEmpty());
 
     if (returnValue.IsEmpty())
         return;
 
-    if (!returnValue->IsNull() && !returnValue->IsUndefined() && event->isBeforeUnloadEvent()) {
+    if (m_isAttribute && !returnValue->IsNull() && !returnValue->IsUndefined() && event->isBeforeUnloadEvent()) {
         V8TRYCATCH_FOR_V8STRINGRESOURCE_VOID(V8StringResource<>, stringReturnValue, returnValue);
         toBeforeUnloadEvent(event)->setReturnValue(stringReturnValue);
     }
 
     if (m_isAttribute && shouldPreventDefault(returnValue))
         event->preventDefault();
 }
 
 bool V8AbstractEventListener::shouldPreventDefault(v8::Local<v8::Value> returnValue)
 {
@@ skipping 15 matching lines @@
         return v8::Local<v8::Object>();
     return v8::Local<v8::Object>::New(isolate, v8::Handle<v8::Object>::Cast(value));
 }
 
 void V8AbstractEventListener::setWeakCallback(const v8::WeakCallbackData<v8::Object, V8AbstractEventListener> &data)
 {
     data.GetParameter()->m_listener.clear();
 }
 
 } // namespace WebCore