[regexp] Implement regexp groups as wrapper.

src/regexp/regexp-parser.cc

Index: src/regexp/regexp-parser.cc
diff --git a/src/regexp/regexp-parser.cc b/src/regexp/regexp-parser.cc
index 3035f6a9a953e6eb5ffe4466e07612f27b6c9996..3621f7d96e4fbf4634b7a214d7beb5defa019eae 100644
--- a/src/regexp/regexp-parser.cc
+++ b/src/regexp/regexp-parser.cc
@@ -216,7 +216,9 @@ RegExpTree* RegExpParser::ParseDisjunction() {
           RegExpCapture* capture = GetCapture(capture_index);
           capture->set_body(body);
           body = capture;
-        } else if (group_type != GROUPING) {
+        } else if (group_type == GROUPING) {
+          body = new (zone()) RegExpGroup(body);
+        } else {
           DCHECK(group_type == POSITIVE_LOOKAROUND ||
                  group_type == NEGATIVE_LOOKAROUND);
           bool is_positive = (group_type == POSITIVE_LOOKAROUND);