Fix detached event listener attribute updating.

third_party/WebKit/Source/bindings/core/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 186 matching lines @@
                                     v8::Local<v8::Object>::Cast(value));
 }
 
 bool V8AbstractEventListener::BelongsToTheCurrentWorld(
     ExecutionContext* execution_context) const {
   if (!GetIsolate()->GetCurrentContext().IsEmpty() &&
       &World() == &DOMWrapperWorld::Current(GetIsolate()))
     return true;
   // If currently parsing, the parser could be accessing this listener
   // outside of any v8 context; check if it belongs to the main world.
-  if (!GetIsolate()->InContext() && execution_context->IsDocument()) {
+  if (!GetIsolate()->InContext() && execution_context &&
+      execution_context->IsDocument()) {
     Document* document = ToDocument(execution_context);
     if (document->Parser() && document->Parser()->IsParsing())
       return World().IsMainWorld();
   }
   return false;
 }
 
 void V8AbstractEventListener::ClearListenerObject() {
   if (!HasExistingListenerObject())
     return;
@@ skipping 13 matching lines @@
 DEFINE_TRACE(V8AbstractEventListener) {
   visitor->Trace(worker_global_scope_);
   EventListener::Trace(visitor);
 }
 
 DEFINE_TRACE_WRAPPERS(V8AbstractEventListener) {
   visitor->TraceWrappers(listener_.Cast<v8::Value>());
 }
 
 }  // namespace blink