Revert removal of shared TaskQueue for page.screenshot()

[dmitrysteblyuk]

Issue #6713.
Please, notice that I changed the return type of page.screenshot() back to Promise<Buffer | string>.
I did it because I couldn't find any place where it returns void.
Let me know if it was a mistake on my part, I'll change it back.

[dmitrysteblyuk]

@jackfranklin sorry for the ping, but Travis appears not to be working for the last 5 days.

[mathiasbynens]

@jackfranklin sorry for the ping, but Travis appears not to be working for the last 5 days.

Yeah, we're aware of this. Travis essentially removed support for their free plan, so we'll have to migrate to GitHub Actions. #6726

[jackfranklin]

@dmitrysteblyuk thank you for this PR and for the bug report. This looks good to me. Now we've landed GitHub actions into the codebase, would you mind rebasing your PR? Then we can see if CI is happy 👍

[jackfranklin]

@mathiasbynens PTAL.

[google-cla]

All (the pull request submitter and all commit authors) CLAs are signed, but one or more commits were authored or co-authored by someone other than the pull request submitter.

We need to confirm that all authors are ok with their commits being contributed to this project. Please have them confirm that by leaving a comment that contains only @googlebot I consent. in this pull request.

Note to project maintainer: There may be cases where the author cannot leave a comment, or the comment is not properly detected as consent. In those cases, you can manually confirm consent of the commit author(s), and set the cla label to yes (if enabled on your project).

ℹ️ Googlers: Go here for more info.

[jschfflr]

@googlebot I consent.