simplify define property by using a helper in playground object getter memoization

lib/6to5/transformation/transformers/playground-object-getter-memoization.js

@@ -3,7 +3,7 @@ var util     = require("../../util");
 var t        = require("../../types");
 
 exports.Property =
-exports.MethodDefinition = function (node) {
+exports.MethodDefinition = function (node, parent, file) {
   if (node.kind !== "memo") return;
   node.kind = "get";
 
@@ -21,10 +21,11 @@ exports.MethodDefinition = function (node) {
       if (t.isFunction(node)) return;
 
       if (t.isReturnStatement(node) && node.argument) {
-        node.argument = t.memberExpression(util.template("object-getter-memoization", {
-          KEY: key,
-          VALUE: node.argument
-        }), key, true);
+        node.argument = t.memberExpression(t.callExpression(file.addDeclaration("define-property"), [
+          t.thisExpression(),
+          key,
+          node.argument
+        ]), key, true);
       }
     }
   });