Fix call of finalized virtual function.

src/ast.cc

Index: src/ast.cc
diff --git a/src/ast.cc b/src/ast.cc
index 8f69bd705923b7e9136d3881ebffca5f4507d9e8..3c968528dde6dad95edb0da3fa94213772d6cc6d 100644
--- a/src/ast.cc
+++ b/src/ast.cc
@@ -967,7 +967,8 @@ void* RegExpUnparser::VisitText(RegExpText* that, void* data) {
     stream()->Add("(!");
     for (int i = 0; i < that->elements()->length(); i++) {
       stream()->Add(" ");
-      that->elements()->at(i).data.u_atom->Accept(this, data);
+      static_cast<RegExpTree*>(that->elements()->at(i).data.u_atom)->Accept(
+          this, data);
     }
     stream()->Add(")");
   }