class ActionView::StreamingFlow

def get(key)

key and yield.
fiber, we set that we are waiting for the given
is not available and we are inside the layout
Try to get stored content. If the content 
def get(key)
  return super if @content.key?(key)
  if inside_fiber?
    view = @view
    begin
      @waiting_for = key
      view.output_buffer, @parent = @child, view.output_buffer
      Fiber.yield
    ensure
      @waiting_for = nil
      view.output_buffer, @child = @parent, view.output_buffer
    end
  end
  super
end