Handle backslashes and newlines when escaping strings.

dart/lib/core/errors.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.
 
 class Error {
   const Error();
 }
 
 class AssertionError implements Error {
 }
@@ skipping 63 matching lines @@
       }
       String formalParameters = sb.toString();
       return "NoSuchMethodError: incorrect number of arguments passed to "
           "method named '$_functionName'\n"
           "Receiver: ${safeToString(_receiver)}\n"
           "Tried calling: $_functionName($actualParameters)\n"
           "Found: $_functionName($formalParameters)";
     }
   }
 
-  external static String safeToString(Object object);
+  static String safeToString(Object object) {
+    if (object is int || object is double || object is bool || null == object) {
+      return object.toString();
+    }
+    if (object is String) {
+      // TODO(ahe): Remove backslash when http://dartbug.com/4995 is fixed.
+      const backslash = '\\';
+      String escaped = object
+        .replaceAll('$backslash', '$backslash$backslash')
+        .replaceAll('\n', '${backslash}n')
+        .replaceAll('\r', '${backslash}r')
+        .replaceAll('"',  '$backslash"');
+      return '"$escaped"';
+    }
+    return _objectToString(object);
+  }
+
+  external static _objectToString(Object object);
 }