Don't overload FreeListElement for become.

runtime/vm/raw_object.h

Index: runtime/vm/raw_object.h
diff --git a/runtime/vm/raw_object.h b/runtime/vm/raw_object.h
index 74cf17600a7960dfc68869a8e14d5e4189738a9e..be3ad3d70e184f286d90a9a360451198f7841ec0 100644
--- a/runtime/vm/raw_object.h
+++ b/runtime/vm/raw_object.h
@@ -184,6 +184,7 @@ CLASS_LIST_TYPED_DATA(DEFINE_OBJECT_KIND)
   // The following entry does not describe a real class, but instead it is an
   // id which is used to identify free list elements in the heap.
   kFreeListElement,
+  kForwardingCorpse,

[Cutch, 2016/06/02 14:09:53]

Add a comment about kForwardingCorpse

[rmacnak, 2016/06/02 17:57:06]

Done.

 
   kNumPredefinedCids,
 };
@@ -442,6 +443,9 @@ CLASS_LIST_TYPED_DATA(DEFINE_IS_CID)
   bool IsFreeListElement() const {
     return ((GetClassId() == kFreeListElement));
   }
+  bool IsForwardingCorpse() const {
+    return ((GetClassId() == kForwardingCorpse));
+  }
 
   intptr_t Size() const {
     uword tags = ptr()->tags_;