Fix issue 571: display descriptive names for code objects from snapshot.

src/serialize.h

Index: src/serialize.h
diff --git a/src/serialize.h b/src/serialize.h
index fcd37230ff7fd91db8fcd621480c125b01a9c9a2..8dd193f5eabd81fe8ebdeeb5878f8989d6aff5a6 100644
--- a/src/serialize.h
+++ b/src/serialize.h
@@ -147,6 +147,8 @@ class SnapshotByteSource {
     return position_ == length_;
   }
 
+  const int position() { return position_; }
+
  private:
   const byte* data_;
   int length_;
@@ -294,6 +296,7 @@ class SnapshotByteSink {
     Put(byte, description);
   }
   void PutInt(uintptr_t integer, const char* description);
+  virtual int Position() = 0;
 };