Request for comments on overall approach.

runtime/vm/snapshot.h

Index: runtime/vm/snapshot.h
diff --git a/runtime/vm/snapshot.h b/runtime/vm/snapshot.h
index ad0f2e07ba8e68ff8318dd5b2f6b83428f1a8c0a..96d5e0b4b188cace19c78bca64431a187eb8dc7e 100644
--- a/runtime/vm/snapshot.h
+++ b/runtime/vm/snapshot.h
@@ -505,16 +505,18 @@ class SnapshotWriter : public BaseWriter {
   // Writes a full snapshot of the Isolate.
   void WriteFullSnapshot();
 
+  uword GetObjectTags(RawObject* raw);
+
  private:
   class ForwardObjectNode : public ZoneAllocated {
    public:
-    ForwardObjectNode(RawObject* raw, RawClass* cls) : raw_(raw), cls_(cls) {}
+    ForwardObjectNode(RawObject* raw, uword tags) : raw_(raw), tags_(tags) {}
     RawObject* raw() const { return raw_; }
-    RawClass* cls() const { return cls_; }
+    uword tags() const { return tags_; }
 
    private:
     RawObject* raw_;
-    RawClass* cls_;
+    uword tags_;
 
     DISALLOW_COPY_AND_ASSIGN(ForwardObjectNode);
   };