title: How to define action='store_true' in absl
body: <p>I am migrating code from argparse to absl (The python version is 3.6). The code using argparse has the following </p>
  
  <pre><code>  parser.add_argument('--flip_left_right', default=False,
    help="flip", action='store_true')
  </code></pre>
  
  <p>Using absl, I can define the flag with the following code</p>
  
  <pre><code>flags.DEFINE_bool("flip_left_right", False, "flip")
  </code></pre>
  
  <p>But I cannot define "action" in absl (which will report error "unexpected keyword argument 'action'" if I do so). How can I define the action='store_true' in absl? Thanks a lot!</p>