Fix compile warning on mac

tools/dom/scripts/systemnative.py

 #!/usr/bin/python
 # 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.
 
 """This module provides shared functionality for the systems to generate
 native binding from the IDL database."""
 
 import emitter
 import os
@@ skipping 432 matching lines @@
         '                             NativeType* value)\n'
         '    {\n'
         '        if (value) {\n'
         '            DartDOMData* domData = static_cast<DartDOMData*>(\n'
         '                Dart_GetNativeIsolateData(args));\n'
         '            Dart_WeakPersistentHandle result =\n'
         '                DartDOMWrapper::lookupWrapper<Dart$(INTERFACE)>(domData, value);\n'
         '            if (result)\n'
         '                Dart_SetWeakHandleReturnValue(args, result);\n'
         '            else {\n'
-        '                DartApiScope apiScope();\n'
+        '                DartApiScope apiScope;\n'
         '                Dart_SetReturnValue(args, createWrapper(domData, value));\n'
         '            }\n'
         '        }\n'
         '    }\n',
         INTERFACE=self._interface.id)
 
     if ('CustomToV8' in ext_attrs or
         'PureInterface' in ext_attrs or
         'CPPPureInterface' in ext_attrs or
         self._interface_type_info.custom_to_dart()):
@@ skipping 838 matching lines @@
     e.Emit("};\n");
     e.Emit('\n');
     e.Emit('} // namespace WebCore\n');
 
 def _IsOptionalStringArgumentInInitEventMethod(interface, operation, argument):
   return (
       interface.id.endswith('Event') and
       operation.id.startswith('init') and
       argument.ext_attrs.get('Default') == 'Undefined' and
       argument.type.id == 'DOMString')