[wrapper-tracing] MutationObserver: Add write barriers

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

Index: third_party/WebKit/Source/core/dom/NodeRareData.h
diff --git a/third_party/WebKit/Source/core/dom/NodeRareData.h b/third_party/WebKit/Source/core/dom/NodeRareData.h
index d3d428f2075f5a80a1edef508e4e3de00bcbd2f8..2e2de6c8c09437299e0171e4debe85a45bfdd97a 100644
--- a/third_party/WebKit/Source/core/dom/NodeRareData.h
+++ b/third_party/WebKit/Source/core/dom/NodeRareData.h
@@ -22,6 +22,7 @@
 #ifndef NodeRareData_h
 #define NodeRareData_h
 
+#include "bindings/core/v8/ScriptWrappableVisitor.h"
 #include "core/dom/MutationObserverRegistration.h"
 #include "core/dom/NodeListsNodeData.h"
 #include "platform/heap/Handle.h"
@@ -84,8 +85,10 @@ class NodeRareData : public GarbageCollectedFinalized<NodeRareData>,
     return m_mutationObserverData.get();
   }
   NodeMutationObserverData& ensureMutationObserverData() {
-    if (!m_mutationObserverData)
+    if (!m_mutationObserverData) {
       m_mutationObserverData = NodeMutationObserverData::create();
+      ScriptWrappableVisitor::writeBarrier(this, m_mutationObserverData);
+    }
     return *m_mutationObserverData;
   }