[bootstrapper] Ensure RegExp constructor has fast properties.

src/bootstrapper.cc

Index: src/bootstrapper.cc
diff --git a/src/bootstrapper.cc b/src/bootstrapper.cc
index a1ffe77db635a8364deb7f1f96754eeba4348d5e..3d5c4d6f49d09bcc7bd8d25350b323fd4830d7cd 100644
--- a/src/bootstrapper.cc
+++ b/src/bootstrapper.cc
@@ -2437,6 +2437,15 @@ void Genesis::InitializeGlobal(Handle<JSGlobalObject> global_object,
     native_context()->set_regexp_last_match_info(*last_match_info);
     Handle<RegExpMatchInfo> internal_match_info = factory->NewRegExpMatchInfo();
     native_context()->set_regexp_internal_match_info(*internal_match_info);
+
+    // Force the RegExp constructor to fast properties, so that we can use the
+    // fast paths for various things like
+    //
+    //   x instanceof RegExp
+    //
+    // etc. We should probably come up with a more principled approach once
+    // the JavaScript builtins are gone.
+    JSObject::MigrateSlowToFast(regexp_fun, 0, "Bootstrapping");
   }
 
   {  // -- E r r o r