Move all the closure related fields in RawFunction into a new class

vm/raw_object.cc

Index: vm/raw_object.cc
===================================================================
--- vm/raw_object.cc	(revision 12230)
+++ vm/raw_object.cc	(working copy)
@@ -374,6 +374,13 @@
 }
 
 
+intptr_t RawClosureData::VisitClosureDataPointers(
+    RawClosureData* raw_obj, ObjectPointerVisitor* visitor) {
+  visitor->VisitPointers(raw_obj->from(), raw_obj->to());
+  return ClosureData::InstanceSize();
+}
+
+
 intptr_t RawFunction::VisitFunctionPointers(RawFunction* raw_obj,
                                             ObjectPointerVisitor* visitor) {
   visitor->VisitPointers(raw_obj->from(), raw_obj->to());