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

tests/compiler/dart2js_extra/string_interpolation_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 that String interpolation works in the code generated by the leg
 // compiler.
 
 
 int ifun() => 37;
 double dfun() => 2.71828;
 bool bfun() => true;
 String sfun() => "sfun";
 void nfun() => null;
 
 
 void testEscapes() {
   // Test that escaping the '$' prevents string interpolation.
   String x = "NOT HERE";
-  Expect.equals(@'a${x}', 'a\${x}');
-  Expect.equals(@'a$x', 'a\$x');
-  Expect.equals(@'a${x}', '''a\${x}''');
-  Expect.equals(@'a$x', '''a\$x''');
-  Expect.equals(@'a${x}', "a\${x}");
-  Expect.equals(@'a$x', "a\$x");
-  Expect.equals(@'a${x}', """a\${x}""");
-  Expect.equals(@'a$x', """a\$x""");
+  Expect.equals(r'a${x}', 'a\${x}');
+  Expect.equals(r'a$x', 'a\$x');
+  Expect.equals(r'a${x}', '''a\${x}''');
+  Expect.equals(r'a$x', '''a\$x''');
+  Expect.equals(r'a${x}', "a\${x}");
+  Expect.equals(r'a$x', "a\$x");
+  Expect.equals(r'a${x}', """a\${x}""");
+  Expect.equals(r'a$x', """a\$x""");
 }
 
 
 void testMultiLine() {
   var a = "string";
   var b = 42;
   var c = 3.1415;
   var d = false;
   var n = null;
 
@@ skipping 80 matching lines @@
   // Lotsa-nested.
   Expect.equals("42", "${'${"${'${"${'${"$b"}'}"}'}"}'}");
 }
 
 
 void main() {
   testSimple();
   testMultiLine();
   testEscapes();
 }