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

tests/compiler/dart2js_native/abstract_class_test.dart

 // Copyright (c) 2013, 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.
 
 import "native_testing.dart";
 
 // Native classes can have subclasses that are not declared to the program.  The
 // subclasses are indistinguishable from the base class.  This means that
 // abstract native classes can appear to have instances.
 
 @Native("A")
 abstract class A {}
 
 @Native("B")
 abstract class B {
   foo() native;
 }
 
 class C {}
 
 makeA() native;
 makeB() native;
 
-void setup() native """
-// This code is all inside 'setup' and so not accessible from the global scope.
-function A(){}
-function B(){}
-B.prototype.foo = function() { return 'B.foo'; };
-makeA = function(){return new A};
-makeB = function(){return new B};
-self.nativeConstructor(A);
-self.nativeConstructor(B);
-""";
+void setup() {
+  JS('', r"""
+(function(){
+  function A(){}
+  function B(){}
+  B.prototype.foo = function() { return 'B.foo'; };
+  makeA = function(){return new A()};
+  makeB = function(){return new B()};
+  self.nativeConstructor(A);
+  self.nativeConstructor(B);
+})()
+""");
+}
 
 main() {
   nativeTesting();
   setup();
 
   var a = makeA();
   var b = makeB();
   var c = confuse(new C());
 
   Expect.isTrue(a is A);
   Expect.isFalse(b is A);
   Expect.isFalse(c is A);
 
   Expect.isFalse(a is B);
   Expect.isTrue(b is B);
   Expect.isFalse(c is B);
 
   Expect.isFalse(a is C);
   Expect.isFalse(b is C);
   Expect.isTrue(c is C);
 
   Expect.equals('B.foo', b.foo());
 }