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

tests/compiler/dart2js_extra/string_escape_test.dart

 // Copyright (c) 2012, 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 escapes work correctly.
 
 testSingleCharacterEscapes() {
   List/*<String>*/ examples = [
     "\b\f\n\r\t\v",
     '\b\f\n\r\t\v',
     """\b\f\n\r\t\v""",
     '''\b\f\n\r\t\v''',
   ];
   List values = [8, 12, 10, 13, 9, 11];
   for (String s in examples) {
     Expect.equals(6, s.length);
     for (int i = 0; i < 6; i++) {
       Expect.equals(values[i], s.charCodeAt(i));
     }
   }
 
   // An escaped quote isn't part of a multiline end quote.
-  Expect.equals(@'"', """\"""");
-  Expect.equals(@"'", '''\'''');
-  Expect.equals(@'" "', """" \"""");
-  Expect.equals(@"' '", '''' \'''');
-  Expect.equals(@'"" ', """"" """);
-  Expect.equals(@"'' ", ''''' ''');
+  Expect.equals(r'"', """\"""");
+  Expect.equals(r"'", '''\'''');
+  Expect.equals(r'" "', """" \"""");
+  Expect.equals(r"' '", '''' \'''');
+  Expect.equals(r'"" ', """"" """);
+  Expect.equals(r"'' ", ''''' ''');
 }
 
 testXEscapes() {
   var allBytes =
       "\x00\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f"
       "\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f"
       "\x20\x21\x22\x23\x24\x25\x26\x27\x28\x29\x2a\x2b\x2c\x2d\x2e\x2f"
       "\x30\x31\x32\x33\x34\x35\x36\x37\x38\x39\x3a\x3b\x3c\x3d\x3e\x3f"
       "\x40\x41\x42\x43\x44\x45\x46\x47\x48\x49\x4a\x4b\x4c\x4d\x4e\x4f"
       "\x50\x51\x52\x53\x54\x55\x56\x57\x58\x59\x5a\x5b\x5c\x5d\x5e\x5f"
@@ skipping 62 matching lines @@
 }
 
 
 testQuotes() {
   // The string [ "' ].
   String bothQuotes = ' "' "' ";
   Expect.equals(bothQuotes, " \"' ");
   Expect.equals(bothQuotes, ' "\' ');
   Expect.equals(bothQuotes, """ "' """);
   Expect.equals(bothQuotes, ''' "' ''');
-  Expect.equals(bothQuotes, @""" "' """);
-  Expect.equals(bothQuotes, @''' "' ''');
+  Expect.equals(bothQuotes, r""" "' """);
+  Expect.equals(bothQuotes, r''' "' ''');
 }
 
 
 testRawStrings() {
-  String raw1 = @'\x00';
+  String raw1 = r'\x00';
   Expect.equals(4, raw1.length);
   Expect.equals(0x5c, raw1.charCodeAt(0));
 }
 
 main() {
   // Test \x??.
   testXEscapes();
   // Test \u???? and \u{?+}.
   testUEscapes();
   // Test \b, \f, \n, \r, \t, \v.
   testSingleCharacterEscapes();
   // Test all other single character (identity) escaeps.
   testIdentityEscapes();
   // Test that quotes are handled correctly.
   testQuotes();
   // Test that raw strings are raw.
   testRawStrings();
 }