Add screenshot and viewport sharing tests

[mudhoney]

Summary

Adds tests for taking and viewing screenshots, and for sharing the viewport.

Testing

Enter the browsers and the output modes (minimal, normal, embed) this change was tested

browser	normal	minimal	embed
firefox	tested	untested	untested
chrome	tested	untested	untested
safari	tested	untested	untested
edge	tested	untested	untested