[regexp] Implement regexp groups as wrapper.

src/regexp/regexp-ast.cc

Index: src/regexp/regexp-ast.cc
diff --git a/src/regexp/regexp-ast.cc b/src/regexp/regexp-ast.cc
index b5c2bb6d91d9f3b060366171a21bf645ff8a805a..85babb1f74e76f8c2b015738d57bc4a895ff4b6c 100644
--- a/src/regexp/regexp-ast.cc
+++ b/src/regexp/regexp-ast.cc
@@ -264,6 +264,12 @@ void* RegExpUnparser::VisitCapture(RegExpCapture* that, void* data) {
   return NULL;
 }
 
+void* RegExpUnparser::VisitGroup(RegExpGroup* that, void* data) {
+  os_ << "(?: ";
+  that->body()->Accept(this, data);
+  os_ << ")";
+  return NULL;
+}
 
 void* RegExpUnparser::VisitLookaround(RegExpLookaround* that, void* data) {
   os_ << "(";