AttributeError: '_ToolBar' object has no attribute 'sizes' on Toggle toolbar

Hi.

I'm getting this exception when I click on Toggle Toolbar:

```
Traceback (most recent call last):
File "/home/sebasmagri/.virtualenvs/rested/lib/python2.7/site-packages/pyface/ui/qt4/action/action_item.py", line 149, in _qt4_on_triggered
self.controller.perform(action)
File "/home/sebasmagri/.virtualenvs/rested/lib/python2.7/site-packages/traitsui/qt4/ui_base.py", line 131, in perform
self.ui.do_undoable( self._perform, action )
File "/home/sebasmagri/.virtualenvs/rested/lib/python2.7/site-packages/traitsui/ui.py", line 708, in do_undoable
action( *args, **kw )
File "/home/sebasmagri/.virtualenvs/rested/lib/python2.7/site-packages/traitsui/qt4/ui_base.py", line 136, in _perform
method( self.ui.info )
File "/home/sebasmagri/.virtualenvs/rested/lib/python2.7/site-packages/rested/rest_editor_view.py", line 635, in toggle_file_browser
sizes = splitter.sizes()
AttributeError: '_ToolBar' object has no attribute 'sizes'
```

If you need more info please let me know.