Fix crash in MutationObserver::canDeliver due to NULL ExecutionContext

Source/core/dom/MutationObserver.cpp

 /*
  * Copyright (C) 2011 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 191 matching lines @@
 WillBeHeapHashSet<RawPtrWillBeMember<Node> > MutationObserver::getObservedNodes() const
 {
     WillBeHeapHashSet<RawPtrWillBeMember<Node> > observedNodes;
     for (MutationObserverRegistrationSet::const_iterator iter = m_registrations.begin(); iter != m_registrations.end(); ++iter)
         (*iter)->addRegistrationNodesToSet(observedNodes);
     return observedNodes;
 }
 
 bool MutationObserver::canDeliver()
 {
-    return !m_callback->executionContext()->activeDOMObjectsAreSuspended();
+    return m_callback->canInvokeCallback();
 }
 
 void MutationObserver::deliver()
 {
     ASSERT(canDeliver());
 
     // Calling clearTransientRegistrations() can modify m_registrations, so it's necessary
     // to make a copy of the transient registrations before operating on them.
     WillBeHeapVector<RawPtrWillBeMember<MutationObserverRegistration>, 1> transientRegistrations;
     for (MutationObserverRegistrationSet::iterator iter = m_registrations.begin(); iter != m_registrations.end(); ++iter) {
@@ skipping 47 matching lines @@
 
 void MutationObserver::trace(Visitor* visitor)
 {
 #if ENABLE(OILPAN)
     visitor->trace(m_records);
     visitor->trace(m_registrations);
 #endif
 }
 
 } // namespace blink