dart2js_native tests: Migrate 'native STRING' to JS-calls

tests/compiler/dart2js_native/native_library_same_name_used_frog_test.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // Test for correct hidden native class when abstract class has same name.
 
 library main;
 
 import 'native_testing.dart';
 import 'native_library_same_name_used_lib1.dart';
 
-void setup() native """
+void setup() {
+  JS('', r"""
+(function(){
   // This code is all inside 'setup' and so not accessible from the global
   // scope.
   function I(){}
   I.prototype.read = function() { return this._x; };
   I.prototype.write = function(x) { this._x = x; };
-  makeI = function(){return new I};
+  makeI = function(){return new I()};
   self.nativeConstructor(I);
-""";
+})()""");
+}
 
 // A pure Dart implementation of I.
 
 class ProxyI implements I {
   ProxyI b;
   ProxyI read() {
     return b;
   }
 
   write(ProxyI x) {
@@ skipping 16 matching lines @@
 
   Expect.isTrue(b1 is I, 'b1 is I');
   Expect.isTrue(b1 is ProxyI, 'b1 is ProxyI');
 
   Expect.isTrue(a1 is I, 'a1 is I');
   Expect.isFalse(a1 is ProxyI, 'a1 is ProxyI');
 
   Expect.isTrue(confuse(a1) is I, 'a1 is I');
   Expect.isFalse(confuse(a1) is ProxyI, 'a1 is ProxyI');
 }