[regexp] Add support for dotAll flag

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 0d0e3ed0ae90d00eca5ba3a17b0c86df985367f4..831b4dd46fc5871b36c9c9d1eb2d21b34da09228 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -16140,6 +16140,13 @@ JSRegExp::Flags RegExpFlagsFromString(Handle<String> flags, bool* success) {
       case 'm':
         flag = JSRegExp::kMultiline;
         break;
+      case 's':
+        if (FLAG_harmony_regexp_dotall) {
+          flag = JSRegExp::kDotAll;
+        } else {
+          return JSRegExp::Flags(0);
+        }
+        break;
       case 'u':
         flag = JSRegExp::kUnicode;
         break;