Ability to clip screenshots

[coyney]

Feature Proposal

Description

Use Case:
Having the ability to clip screenshots to specific x, y, width, and height values would result in being able to have lower storage requirements as only the part of the page that you require is stored.

Puppeteer have the option here, is there anyway to pass this value through?
https://github.com/GoogleChrome/puppeteer/blob/master/docs/api.md#pagescreenshotoptions