Don't write generated C++ bindings twice, only once.

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 1213 matching lines @@
     e.Emit('    bool is_node;\n');
     e.Emit('    bool is_active;\n');
     e.Emit('    bool is_event;\n');
     e.Emit('} _Classinfo;\n');
     e.Emit('typedef _Classinfo _DartWebkitClassInfo[NumWebkitClassIds];\n');
     e.Emit('\n');
     e.Emit('extern _DartWebkitClassInfo DartWebkitClassInfo;\n');
     e.Emit('\n');
     e.Emit('} // namespace WebCore\n');
     e.Emit('#endif // DartWebkitClassIds_h\n');
-    self._emitters.Flush()
 
     path = os.path.join(output_dir, 'DartWebkitClassIds.cpp')
     e = self._emitters.FileEmitter(path)
     e.Emit('// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file\n');
     e.Emit('// for details. All rights reserved. Use of this source code is governed by a\n');
     e.Emit('// BSD-style license that can be found in the LICENSE file.\n');
     e.Emit('// WARNING: Do not edit - generated code.\n');
     e.Emit('// See dart/tools/dom/scripts/systemnative.py\n');
     e.Emit('\n');
     e.Emit('#include "DartWebkitClassIds.h"\n');
@@ skipping 29 matching lines @@
         e.Emit(' %sClassId,\n' % supertype)
       else:
         e.Emit(' -1,')
       e.Emit(" %s," % TypeCheckHelper(is_node_test))
       e.Emit(" %s," % TypeCheckHelper(is_active_test))
       e.Emit(" %s," % TypeCheckHelper(is_event_target_test))
       e.Emit(" },\n")
     e.Emit("};\n");
     e.Emit('\n');
     e.Emit('} // namespace WebCore\n');
-    self._emitters.Flush()
 
 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')