migrate raw string to new syntax in html

lib/html/dart2js/html_dart2js.dart

Index: lib/html/dart2js/html_dart2js.dart
===================================================================
--- lib/html/dart2js/html_dart2js.dart	(revision 12745)
+++ lib/html/dart2js/html_dart2js.dart	(working copy)
@@ -31,7 +31,7 @@
 }
 
 // Support for Send/ReceivePortSync.
-int _getNewIsolateId() native @'''
+int _getNewIsolateId() native r'''
   if (!window.$dart$isolate$counter) {
     window.$dart$isolate$counter = 1;
   }
@@ -40,7 +40,7 @@
 
 // Fast path to invoke JS send port.
 _callPortSync(int id, message) {
-  return JS('var', @'ReceivePortSync.dispatchCall(#, #)', id, message);
+  return JS('var', r'ReceivePortSync.dispatchCall(#, #)', id, message);
 }
 
 // TODO(vsm): Plumb this properly.
@@ -41556,7 +41556,7 @@
 bool _isJavaScriptSimpleObject(value) =>
     JS('bool', 'Object.getPrototypeOf(#) === Object.prototype', value);
 bool _isImmutableJavaScriptArray(value) =>
-    JS('bool', @'!!(#.immutable$list)', value);
+    JS('bool', r'!!(#.immutable$list)', value);
 // 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.