Support redirecting factory constructors in the VM (issue 3969).

runtime/vm/raw_object.cc

Index: runtime/vm/raw_object.cc
===================================================================
--- runtime/vm/raw_object.cc	(revision 12790)
+++ runtime/vm/raw_object.cc	(working copy)
@@ -381,6 +381,13 @@
 }
 
 
+intptr_t RawRedirectionData::VisitRedirectionDataPointers(
+    RawRedirectionData* raw_obj, ObjectPointerVisitor* visitor) {
+  visitor->VisitPointers(raw_obj->from(), raw_obj->to());
+  return RedirectionData::InstanceSize();
+}
+
+
 intptr_t RawFunction::VisitFunctionPointers(RawFunction* raw_obj,
                                             ObjectPointerVisitor* visitor) {
   visitor->VisitPointers(raw_obj->from(), raw_obj->to());