issue 4817 fixed. Implemented raw strings with 'r' instead of '@' for dart2js

tests/compiler/dart2js_foreign/native_class_inheritance4_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.
 
 // Additional Dart code may be 'placed on' hidden native classes.  With
 // inheritance, the superclass method must not be reached by a call on the
 // subclass.
 
 @native("*A")
 class A  {
@@ skipping 11 matching lines @@
 
   int get X => _field2;
   void set X(int x) { _field2 = x; }
 
   int method(int z) => _field2 + z;
 }
 
 @native A makeA() { return new A(); }
 @native B makeB() { return new B(); }
 
-@native(@"""
+@native(r"""
 function inherits(child, parent) {
   if (child.prototype.__proto__) {
     child.prototype.__proto__ = parent.prototype;
   } else {
     function tmp() {};
     tmp.prototype = parent.prototype;
     child.prototype = new tmp();
     child.prototype.constructor = child;
   }
 }
@@ skipping 96 matching lines @@
 }
 
 main() {
   testBasicA_dynamic();
   testBasicA_typed();
   testBasicB_dynamic();
   testBasicB_typed();
   testAB_dynamic();
   testAB_typed();
 }