Virtually dispatched specialized scavengers.

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index 0e455508456d7b23465fa893194b51993e316c78..e764e39fcc5a83c2ed2a57629285b15ec3f1263c 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -2060,6 +2060,23 @@ void ExternalFloatArray::set(int index, float value) {
   ptr[index] = value;
 }
 
+inline Scavenger Map::scavenger() {
+  Scavenger callback = reinterpret_cast<Scavenger>(
+      READ_INTPTR_FIELD(this, kIterateBodyCallbackOffset));
+
+  ASSERT(callback == Heap::GetScavenger(instance_type(),
+                                        instance_size()));
+
+  return callback;
+}
+
+inline void Map::set_scavenger(Scavenger callback) {
+  ASSERT(!reinterpret_cast<Object*>(
+      reinterpret_cast<intptr_t>(callback))->IsHeapObject());
+  WRITE_INTPTR_FIELD(this,
+                     kIterateBodyCallbackOffset,
+                     reinterpret_cast<intptr_t>(callback));
+}
 
 int Map::instance_size() {
   return READ_BYTE_FIELD(this, kInstanceSizeOffset) << kPointerSizeLog2;