Preserve marking bits across scavenges if incremental marker is running.

src/objects-visiting.h

Index: src/objects-visiting.h
diff --git a/src/objects-visiting.h b/src/objects-visiting.h
index e7d3c49dda19292b9ff06fcf70b4b770007b897a..1c569c0cc8849dc75c81a3011cb680d524f3db57 100644
--- a/src/objects-visiting.h
+++ b/src/objects-visiting.h
@@ -142,6 +142,12 @@ class StaticVisitorBase : public AllStatic {
 template<typename Callback>
 class VisitorDispatchTable {
  public:
+  void CopyFrom(VisitorDispatchTable* other) {
+    memcpy(callbacks_,
+           other->callbacks_,
+           kPointerSize*StaticVisitorBase::kVisitorIdCount);
+  }
+
   inline Callback GetVisitor(Map* map) {
     return callbacks_[map->visitor_id()];
   }