Chatter pushdown fails with AttributeError: 'Layout' object has no attribute 'chatter_url'

[Paul Everitt]

When clicking "Chatter" I don't get a pushdown appearing. Perhaps we need a way to gracefully handle failures?

 Instead I get:

Exception at http://localhost:6543/pg/chatter.json?needsTemplate=true&ts=
traceback url: http://localhost:6543/pg/_debug_toolbar/exception?token=84b4ffc522766ea566f5&tb=4527384144
Traceback (most recent call last):
  File "/Users/paul/projects/karl/dev-buildout/eggs/pyramid_debugtoolbar-0.9.8-py2.7.egg/pyramid_debugtoolbar/toolbar.py", line 115, in toolbar_tween
    response = _handler(request)
  File "/Users/paul/projects/karl/dev-buildout/eggs/pyramid_debugtoolbar-0.9.8-py2.7.egg/pyramid_debugtoolbar/panels/performance.py", line 55, in resource_timer_handler
    result = handler(request)
  File "/Users/paul/projects/karl/dev-buildout/eggs/pyramid-1.2.1-py2.7.egg/pyramid/tweens.py", line 17, in excview_tween
    response = handler(request)
  File "/Users/paul/projects/karl/dev-buildout/eggs/pyramid-1.2.1-py2.7.egg/pyramid/router.py", line 153, in handle_request
    response = view_callable(context, request)
  File "/Users/paul/projects/karl/dev-buildout/eggs/pyramid-1.2.1-py2.7.egg/pyramid/config/views.py", line 292, in rendered_view
    result = view(context, request)
  File "/Users/paul/projects/karl/dev-buildout/src/karl/karl/ux2/pushdowns.py", line 80, in chatter_ajax_view
    'chatter_url': layout.chatter_url,
AttributeError: 'Layout' object has no attribute 'chatter_url'