[regexp] Fix passing all flags to RegExp construction

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index b9366c18acbac87f4a19fb76d7b2e5197129b304..4f6e1cd291056ce2ccf2ad53b6c151c1821e8dc0 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -7416,9 +7416,12 @@ class JSRegExp: public JSObject {
     kSticky = 1 << 3,
     kUnicode = 1 << 4,
     kDotAll = 1 << 5,
+    // Update FlagCount when adding new flags.
   };
   typedef base::Flags<Flag> Flags;
 
+  static int FlagCount() { return FLAG_harmony_regexp_dotall ? 6 : 5; }
+
   DECL_ACCESSORS(data, Object)
   DECL_ACCESSORS(flags, Object)
   DECL_ACCESSORS(source, Object)