Add support for BeforeUnloadEvent

Source/core/dom/Event.h

Index: Source/core/dom/Event.h
diff --git a/Source/core/dom/Event.h b/Source/core/dom/Event.h
index 7f705c42d7eb92af109a4f0c66cf63e374db1870..967c934465fde761adecbbb0a0291fb1751ed0f1 100644
--- a/Source/core/dom/Event.h
+++ b/Source/core/dom/Event.h
@@ -124,8 +124,8 @@ public:
     // IE Extensions
     EventTarget* srcElement() const { return target(); } // MSIE extension - "the object that fired the event"
 
-    bool returnValue() const { return !defaultPrevented(); }
-    void setReturnValue(bool returnValue) { setDefaultPrevented(!returnValue); }
+    bool legacyReturnValue() const { return !defaultPrevented(); }
+    void setLegacyReturnValue(bool returnValue) { setDefaultPrevented(!returnValue); }
 
     Clipboard* clipboardData() const { return isClipboardEvent() ? clipboard() : 0; }
 
@@ -146,6 +146,8 @@ public:
     virtual bool isClipboardEvent() const;
     virtual bool isBeforeTextInsertedEvent() const;
 
+    virtual bool isBeforeUnloadEvent() const;
+
     bool propagationStopped() const { return m_propagationStopped || m_immediatePropagationStopped; }
     bool immediatePropagationStopped() const { return m_immediatePropagationStopped; }
 
@@ -169,9 +171,6 @@ public:
     EventPath& eventPath() { return m_eventPath; }
     PassRefPtr<NodeList> path() const;
 
-    virtual bool storesResultAsString() const;
-    virtual void storeResult(const String&);
-
     virtual Clipboard* clipboard() const { return 0; }
 
     bool isBeingDispatched() const { return eventPhase(); }