Feature Request: Pass boolean to the storyFn when being run by puppeteer

[nickradford]

Disclaimer: Love this project, combined with reg-suit, it's amazing.

It would be very nice if during the execution of storybook-chrome-screenshot, the withScreenshot decorator would pass a boolean to the story, which can be used to determine properties to pass to your components. An example would be if I were using the material UI tooltip in some of my UI, and I wanted it to be open in the screenshot pass, but not when I normally use storybook.

storiesOf('SomeComponent', module)
  .add('this one is showing tooltips open', withScreenshot()(props =>(
    <Tooltip open={props.isScreenshot} title="Can't do that now">
      <Button>Disabled</Button>
    </Tooltip>
  ))

[Quramy]

I added the function isScreenshot to get whether the current process is in the screenshot browser:

import { isScreenshot } from 'storycap';

storiesOf('SomeComponent', module)
  .add('this one is showing tooltips open', withScreenshot()(props =>(
    <Tooltip open={isScreenshot()} title="Can't do that now">
      <Button>Disabled</Button>
    </Tooltip>
  ))