support new.target (#4746)

fixes #4745

lib/ast.js

@@ -1812,10 +1812,17 @@ var AST_Super = DEFNODE("Super", null, {
 var AST_This = DEFNODE("This", null, {
     $documentation: "The `this` symbol",
     _validate: function() {
-        if (this.name !== "this") throw new Error('name must be "this"');
+        if (this.TYPE == "This" && this.name !== "this") throw new Error('name must be "this"');
     },
 }, AST_ObjectIdentity);
 
+var AST_NewTarget = DEFNODE("NewTarget", null, {
+    $documentation: "The `new.target` symbol",
+    _validate: function() {
+        if (this.name !== "new.target") throw new Error('name must be "new.target": ' + this.name);
+    },
+}, AST_This);
+
 var AST_Template = DEFNODE("Template", "expressions strings tag", {
     $documentation: "A template literal, i.e. tag`str1${expr1}...strN${exprN}strN+1`",
     $propdoc: {