Oilpan: Prepare to move IdTargetObserver and IdTargetObserverRegistry to Oilpan heap.

Source/core/dom/IdTargetObserver.cpp

Index: Source/core/dom/IdTargetObserver.cpp
diff --git a/Source/core/dom/IdTargetObserver.cpp b/Source/core/dom/IdTargetObserver.cpp
index 50294e4db3c126fa2ae91c6443ea4b9a04610f5d..7f2d3559dbbaabd645eeb3c123f8a90ada9ee849 100644
--- a/Source/core/dom/IdTargetObserver.cpp
+++ b/Source/core/dom/IdTargetObserver.cpp
@@ -31,23 +31,28 @@
 namespace WebCore {
 
 IdTargetObserver::IdTargetObserver(IdTargetObserverRegistry& registry, const AtomicString& id)
-    : m_registry(registry)
+    : m_registry(&registry)
     , m_id(id)
 {
-    m_registry.addObserver(m_id, this);
+    m_registry->addObserver(m_id, this);
 }
 
 IdTargetObserver::~IdTargetObserver()
 {
 #if !ENABLE(OILPAN)
-    m_registry.removeObserver(m_id, this);
+    m_registry->removeObserver(m_id, this);
 #endif
 }
 
+void IdTargetObserver::trace(Visitor* visitor)
+{
+    visitor->trace(m_registry);
+}
+
 void IdTargetObserver::unregister()
 {
 #if ENABLE(OILPAN)
-    m_registry.removeObserver(m_id, this);
+    m_registry->removeObserver(m_id, this);
 #endif
 }