Oilpan: Remove guardRef and guardDeref from TreeScope.

Source/core/dom/DocumentMarkerController.cpp

Index: Source/core/dom/DocumentMarkerController.cpp
diff --git a/Source/core/dom/DocumentMarkerController.cpp b/Source/core/dom/DocumentMarkerController.cpp
index 72e0133386837481c3deaa96ea610f5da47525ed..7ad6fcc2f351d7947056dcd16101c6be0250a3eb 100644
--- a/Source/core/dom/DocumentMarkerController.cpp
+++ b/Source/core/dom/DocumentMarkerController.cpp
@@ -371,6 +371,17 @@ void DocumentMarkerController::removeMarkers(Node* node, unsigned startOffset, i
         node->renderer()->repaint();
 }
 
+void DocumentMarkerController::clearWeakMembers(Visitor* visitor)
+{
+    Vector<const Node*> deadNodes;
+    for (MarkerMap::iterator it = m_markers.begin(); it != m_markers.end(); ++it) {
+        if (!visitor->isAlive(it->key))
+            deadNodes.append(it->key);
+    }
+    for (unsigned i = 0; i < deadNodes.size(); ++i)
+        removeMarkers(const_cast<Node*>(deadNodes[i]));
+}
+
 DocumentMarker* DocumentMarkerController::markerContainingPoint(const LayoutPoint& point, DocumentMarker::MarkerType markerType)
 {
     if (!possiblyHasMarkers(markerType))