Update peg parser tests to r'' strings

utils/tests/peg/peg_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.
 
 #library("peg_tests");
 #import('../../peg/pegparser.dart');
 
 testParens() {
   Grammar g = new Grammar();
   Symbol a = g['A'];
@@ skipping 25 matching lines @@
 
   var a = MANY(TEXT('x'));
 
   g.whitespace = OR([g.whitespace, blockComment]);
 
   check(g, a, "x /**/ x", '[x,x]');
   check(g, a, "x /*/**/*/ x", '[x,x]');
   check(g, a, "x /*/***/ x", 'EOF in block comment');
   check(g, a, "x /*/*/x**/**/ x", '[x,x]');
 
-  check(g, a, @"""
+  check(g, a, r"""
 /* Comment */
 /* Following comment with /* nested comment*/ */
 x
 /* x in comment */
 x /* outside comment */
 """,
         '[x,x]');
 }
 
 testTEXT() {
@@ skipping 62 matching lines @@
   Symbol mult_e = g['mult_e'];
   Symbol add_e = g['add_e'];
   Symbol shift_e = g['shift_e'];
   Symbol relational_e = g['relational_e'];
   Symbol equality_e = g['equality_e'];
   Symbol cond_e = g['cond_e'];
   Symbol assignment_e = g['assignment_e'];
 
   // Lexical elements.
   var idStartChar = CHAR(
-      @"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz");
+      r"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz");
   var idNextChar = CHAR(
-      @"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789$_");
+      r"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789$_");
 
   var id = TEXT(LEX('identifier', [idStartChar, MANY(idNextChar, min: 0)]));
 
   var lit = TEXT(LEX('literal', MANY(CHAR('0123456789'))));
 
 
   var type_name = id;
 
 
   // Expression grammar.
@@ skipping 196 matching lines @@
 }
 
 main() {
   testCODE();
   testParens();
   testOR();
   testTEXT();
   testBlockComment();
   testC();
 }