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

tests/compiler/dart2js_native/native_exceptions1_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.
 
 import 'native_testing.dart';
 
 // Test that hidden native exception classes can be marked as existing.
 //
 // To infer which native hidden types exist, we need
 //   (1) return types of native methods and getters
@@ skipping 22 matching lines @@
 }
 
 // This class is here just so that a dynamic context is polymorphic.
 class B {
   int get code => 666;
   op(String x) => 123;
 }
 
 makeA() native;
 
-void setup1() native """
-// Ensure we are not relying on global names 'A' and 'E'.
-A = null;
-E = null;
-""";
+void setup1() {
+  JS('', r"""
+(function(){
+  // Ensure we are not relying on global names 'A' and 'E'.
+  A = null;
+  E = null;
+})()""");
+}
 
-void setup2() native """
+void setup2() {
+  JS('', r"""
+(function(){
 // This code is all inside 'setup2' and so not accessible from the global scope.
 function E(x){ this.code = x; }
 
 function A(){}
 A.prototype.op = function (x) {
   if (x & 1) throw new E(100);
   return  x / 2;
 };
-makeA = function(){return new A};
+makeA = function(){return new A()};
 
 self.nativeConstructor(E);
 self.nativeConstructor(A);
-""";
+})()""");
+}
 
 int inscrutable(int x) => x == 0 ? 0 : x | inscrutable(x & (x - 1));
 
 main() {
   nativeTesting();
   setup1();
   setup2();
 
   var things = [makeA(), new B()];
   var a = things[inscrutable(0)];
@@ skipping 24 matching lines @@
   threw = false;
   try {
     var x = aa.op(51);
   } on E catch (e) {
     threw = true;
     Expect.equals(100, e.code);
     Expect.isTrue(e is E);
   }
   Expect.isTrue(threw);
 }