Avoid map transitions and multiple backing arrays for builtin prototypes...

src/runtime.cc

Index: src/runtime.cc
===================================================================
--- src/runtime.cc	(revision 2674)
+++ src/runtime.cc	(working copy)
@@ -1022,6 +1022,30 @@
 }
 
 
+static Object* Runtime_OptimizeObjectForAddingMultipleProperties(
+    Arguments args) {
+  HandleScope scope;
+  ASSERT(args.length() == 2);
+  CONVERT_ARG_CHECKED(JSObject, object, 0);
+  CONVERT_SMI_CHECKED(properties, args[1]);
+  if (object->HasFastProperties()) {
+    NormalizeProperties(object, KEEP_INOBJECT_PROPERTIES, properties);
+  }
+  return *object;
+}
+
+
+static Object* Runtime_TransformToFastProperties(Arguments args) {
+  HandleScope scope;
+  ASSERT(args.length() == 1);
+  CONVERT_ARG_CHECKED(JSObject, object, 0);
+  if (!object->HasFastProperties() && !object->IsGlobalObject()) {
+    TransformToFastProperties(object, 0);
+  }
+  return *object;
+}
+
+
 static Object* Runtime_RegExpExec(Arguments args) {
   HandleScope scope;
   ASSERT(args.length() == 4);