wrap helper in feature flag

packages/external-helpers/lib/external-helpers.js

@@ -1,31 +1,36 @@
 import { DEBUG } from '@glimmer/env';
+import { EMBER_NATIVE_DECORATOR_SUPPORT } from '@ember/canary-features';
 
 const setPrototypeOf = Object.setPrototypeOf;
 
-var nativeWrapperCache = new Map();
+export let wrapNativeSuper;
 
-// Super minimal version of Babel's wrapNativeSuper. We only use this for
-// extending Function, for ComputedDecoratorImpl and AliasDecoratorImpl. We know
-// we will never directly create an instance of these classes so no need to
-// include `construct` code or other helpers.
-export function wrapNativeSuper(Class) {
-  if (nativeWrapperCache.has(Class)) {
-    return nativeWrapperCache.get(Class);
-  }
+if (EMBER_NATIVE_DECORATOR_SUPPORT) {
+  var nativeWrapperCache = new Map();
 
-  function Wrapper() {}
-  Wrapper.prototype = Object.create(Class.prototype, {
-    constructor: {
-      value: Wrapper,
-      enumerable: false,
-      writable: true,
-      configurable: true,
-    },
-  });
+  // Super minimal version of Babel's wrapNativeSuper. We only use this for
+  // extending Function, for ComputedDecoratorImpl and AliasDecoratorImpl. We know
+  // we will never directly create an instance of these classes so no need to
+  // include `construct` code or other helpers.
+  wrapNativeSuper = function(Class) {
+    if (nativeWrapperCache.has(Class)) {
+      return nativeWrapperCache.get(Class);
+    }
+
+    function Wrapper() {}
+    Wrapper.prototype = Object.create(Class.prototype, {
+      constructor: {
+        value: Wrapper,
+        enumerable: false,
+        writable: true,
+        configurable: true,
+      },
+    });
 
-  nativeWrapperCache.set(Class, Wrapper);
+    nativeWrapperCache.set(Class, Wrapper);
 
-  return setPrototypeOf(Wrapper, Class);
+    return setPrototypeOf(Wrapper, Class);
+  };
 }
 
 export function classCallCheck(instance, Constructor) {