Tweak toString() for better type inference

tools/dom/templates/html/impl/impl_DOMException.darttemplate

 // Copyright (c) 2013, 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.
 
 part of $LIBRARYNAME;
 
 $(ANNOTATIONS)$(NATIVESPEC)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS {
 
   static const String INDEX_SIZE = 'IndexSizeError';
   static const String HIERARCHY_REQUEST = 'HierarchyRequestError';
@@ skipping 23 matching lines @@
     // Although Safari nightly has updated the name to SecurityError, Safari 5
     // and 6 still return SECURITY_ERR.
     if (Device.isWebKit && errorName == 'SECURITY_ERR') return 'SecurityError';
     // Chrome release still uses old string, remove this line when Chrome stable
     // also prints out SyntaxError.
     if (Device.isWebKit && errorName == 'SYNTAX_ERR') return 'SyntaxError';
     return errorName;
   }
 $endif
 $!MEMBERS
+$if DART2JS
+  @DomName('DOMException.toString')
+  @DocsEditable()
+  String toString() => JS('String', 'String(#)', this);
+$endif
 }