Add ES2015 RegExp full subclassing semantics behind a flag

src/js/i18n.js

Index: src/js/i18n.js
diff --git a/src/js/i18n.js b/src/js/i18n.js
index 10afa7f070c0ba614266f2a75f216e852cd742b0..cbb664b526973beb6bb7df7d1fc256b31a4e511d 100644
--- a/src/js/i18n.js
+++ b/src/js/i18n.js
@@ -36,6 +36,7 @@ var MathFloor;
 var ObjectDefineProperties = utils.ImportNow("ObjectDefineProperties");
 var ObjectDefineProperty = utils.ImportNow("ObjectDefineProperty");
 var ObjectHasOwnProperty = utils.ImportNow("ObjectHasOwnProperty");
+var OverrideFunction = utils.OverrideFunction;
 var patternSymbol = utils.ImportNow("intl_pattern_symbol");
 var RegExpTest;
 var resolvedSymbol = utils.ImportNow("intl_resolved_symbol");
@@ -70,17 +71,6 @@ utils.Import(function(from) {
 
 // Utilities for definitions
 
-function OverrideFunction(object, name, f) {
-  %CheckIsBootstrapping();
-  ObjectDefineProperty(object, name, { value: f,
-                                       writeable: true,
-                                       configurable: true,
-                                       enumerable: false });
-  %FunctionSetName(f, name);
-  %FunctionRemovePrototype(f);
-  %SetNativeFlag(f);
-}
-
 function InstallFunction(object, name, func) {
   InstallFunctions(object, DONT_ENUM, [name, func]);
 }