Gracefully handle property enumeration over deleted plugins.

Source/bindings/core/v8/V8NPObject.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 355 matching lines @@
     NPIdentifier identifier = _NPN_GetIntIdentifier(index);
     v8SetReturnValue(info, npObjectSetProperty(self, identifier, value, info.GetIsolate()));
 }
 
 void npObjectPropertyEnumerator(const v8::PropertyCallbackInfo<v8::Array>& info, bool namedProperty)
 {
     NPObject* npObject = v8ObjectToNPObject(info.Holder());
 
     // Verify that our wrapper wasn't using a NPObject which
     // has already been deleted.
-    if (!npObject || !_NPN_IsAlive(npObject))
+    if (!npObject || !_NPN_IsAlive(npObject)) {
         V8ThrowException::throwReferenceError("NPObject deleted", info.GetIsolate());
+        return;
+    }
 
     if (NP_CLASS_STRUCT_VERSION_HAS_ENUM(npObject->_class) && npObject->_class->enumerate) {
         uint32_t count;
         NPIdentifier* identifiers;
         if (npObject->_class->enumerate(npObject, &identifiers, &count)) {
             uint32_t propertiesCount = 0;
             for (uint32_t i = 0; i < count; ++i) {
                 IdentifierRep* identifier = static_cast<IdentifierRep*>(identifiers[i]);
                 if (namedProperty == identifier->m_isString)
                     ++propertiesCount;
@@ skipping 98 matching lines @@
     v8::HandleScope scope(isolate);
     v8::Handle<v8::Object> wrapper = staticNPObjectMap().newLocal(object, isolate);
     if (!wrapper.IsEmpty()) {
         V8DOMWrapper::clearNativeInfo(wrapper, npObjectTypeInfo());
         staticNPObjectMap().removeAndDispose(object);
         _NPN_ReleaseObject(object);
     }
 }
 
 } // namespace blink