Factor out handling of mixed objects preprocessing after migration

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 1ccdf3b4a51f7d88e7b0f0a3303ebb06b95fe64e..3302a176318d609afb85d57f170a8223d48642d4 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -1359,6 +1359,11 @@ void Heap::MarkCompactPrologue() {
 }
 
 
+void Heap::MigrateMixedObjectInNewSpaceEpilog(HeapObject* dst) {
+  DCHECK(dst->MayContainMixedValues());
+}
+
+
 // Helper class for copying HeapObjects
 class ScavengeVisitor : public ObjectVisitor {
  public:
@@ -2124,6 +2129,10 @@ class ScavengingVisitor : public StaticVisitorBase {
     // Copy the content of source to target.
     heap->CopyBlock(target->address(), source->address(), size);
 
+    if (target->MayContainMixedValues()) {
+      heap->MigrateMixedObjectInNewSpaceEpilog(target);
+    }
+
     // Set the forwarding address.
     source->set_map_word(MapWord::FromForwardingAddress(target));