title: What is the sequence of SessionRunHook's member function to be called?
body: <p>After read the <a href="https://www.tensorflow.org/versions/master/api_docs/python/tf/train/SessionRunHook" rel="noreferrer">API DOC</a>, I also can't understand the usage of SessionRunHook. For example, what is the sequence of SessionRunHook's member 
  function to be called? Is it <code>after_create_session -&gt; before_run -&gt; begin -&gt; after_run -&gt; end</code> ?
  And I can't find the tutorial with detailed examples, is there more detailed explanation?</p>