Set target style variables.
    
    Expected usage: 
      style_loss = StyleLoss(style_layers)
      ...
      init_op = tf.global_variables_initializer()
      init_op.run()
      
      feeds = {... session.run() 'feeds' argument that will make 'style_layers'
               tensors evaluate to activation values of style image...}
      style_loss.set_style(feeds)  # this must be called after 'init_op.run()'

def set_style(self, input_feeds):
    """Set target style variables.
    
    Expected usage: 
      style_loss = StyleLoss(style_layers)
      ...
      init_op = tf.global_variables_initializer()
      init_op.run()
      
      feeds = {... session.run() 'feeds' argument that will make 'style_layers'
               tensors evaluate to activation values of style image...}
      style_loss.set_style(feeds)  # this must be called after 'init_op.run()'
    """
    sess = tf.get_default_session()
    computed = sess.run(self.input_grams, input_feeds)
    for v, g in zip(self.target_vars, computed):
      v.load(g)