Fix mac after https://codereview.chromium.org/1419623003/

snapshot/handle_snapshot.h

Index: snapshot/handle_snapshot.h
diff --git a/snapshot/handle_snapshot.h b/snapshot/handle_snapshot.h
index b86706e7f5e1268f56a01b7862fc2b4db94b7534..1346b41d0df68f87b59291f795c362d0e0551b50 100644
--- a/snapshot/handle_snapshot.h
+++ b/snapshot/handle_snapshot.h
@@ -25,8 +25,8 @@ struct HandleSnapshot {
   HandleSnapshot();
   ~HandleSnapshot();
 
-  //! \brief A string representation of the handle's type.
-  std::wstring type_name;
+  //! \brief A UTF-8 string representation of the handle's type.
+  std::string type_name;
 
   //! \brief The handle's value.
   uint32_t handle;