Tweak toString() for better type inference

tools/dom/templates/html/impl/impl_Location.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;
 
 @DocsEditable()
 $(ANNOTATIONS)$(NATIVESPEC)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS {
 $!MEMBERS
 
 $if DART2JS
   @DomName('Location.origin')
   String get origin {
     if (JS('bool', '("origin" in #)', this)) {
       return JS('String', '#.origin', this);
     }
     return '${this.protocol}//${this.host}';
   }
 $endif
+
+$if DART2JS
+  @DomName('Location.toString')
+  @DocsEditable()
+  String toString() => JS('String', 'String(#)', this);
+$endif
 }