MutationObserver: Fix a null-pointer dereference in MutationObserverRegistration::unregister.

third_party/WebKit/Source/core/dom/MutationObserverRegistration.h

 /*
  * 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 15 matching lines @@
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef MutationObserverRegistration_h
 #define MutationObserverRegistration_h
 
 #include "bindings/core/v8/ScriptWrappable.h"
 #include "bindings/core/v8/TraceWrapperMember.h"
+#include "core/CoreExport.h"
 #include "core/dom/MutationObserver.h"
 #include "platform/heap/Handle.h"
 #include "wtf/HashSet.h"
 #include "wtf/text/AtomicString.h"
 #include "wtf/text/AtomicStringHash.h"
 
 namespace blink {
 
 class QualifiedName;
 
-class MutationObserverRegistration final
+class CORE_EXPORT MutationObserverRegistration final
     : public GarbageCollectedFinalized<MutationObserverRegistration>,
       public TraceWrapperBase {
  public:
   static MutationObserverRegistration* create(
       MutationObserver&,
       Node*,
       MutationObserverOptions,
       const HashSet<AtomicString>& attributeFilter);
   ~MutationObserverRegistration();
 
@@ skipping 40 matching lines @@
   typedef HeapHashSet<Member<Node>> NodeHashSet;
   Member<NodeHashSet> m_transientRegistrationNodes;
 
   MutationObserverOptions m_options;
   HashSet<AtomicString> m_attributeFilter;
 };
 
 }  // namespace blink
 
 #endif  // MutationObserverRegistration_h