puppeteer: Add screenshot method to common module.
puppeteer: Add screenshot method to common module.

This will be useful for debugging purposes and we'll use it to take
a screenshot on failure.

shubhamdhama/zulip,synicalsyntax/zulip,eeshangarg/zulip,brainwane/zulip,rht/zulip,rht/zulip,showell/zulip,hackerkid/zulip,brainwane/zulip,eeshangarg/zulip,brainwane/zulip,hackerkid/zulip,synicalsyntax/zulip,rht/zulip,shubhamdhama/zulip,punchagan/zulip,andersk/zulip,punchagan/zulip,kou/zulip,zulip/zulip,brainwane/zulip,zulip/zulip,zulip/zulip,punchagan/zulip,hackerkid/zulip,zulip/zulip,rht/zulip,punchagan/zulip,kou/zulip,synicalsyntax/zulip,rht/zulip,hackerkid/zulip,showell/zulip,brainwane/zulip,shubhamdhama/zulip,andersk/zulip,andersk/zulip,synicalsyntax/zulip,eeshangarg/zulip,kou/zulip,punchagan/zulip,shubhamdhama/zulip,punchagan/zulip,timabbott/zulip,showell/zulip,shubhamdhama/zulip,eeshangarg/zulip,timabbott/zulip,synicalsyntax/zulip,eeshangarg/zulip,showell/zulip,rht/zulip,synicalsyntax/zulip,shubhamdhama/zulip,andersk/zulip,hackerkid/zulip,andersk/zulip,kou/zulip,punchagan/zulip,brainwane/zulip,andersk/zulip,shubhamdhama/zulip,showell/zulip,andersk/zulip,brainwane/zulip,rht/zulip,showell/zulip,timabbott/zulip,kou/zulip,kou/zulip,zulip/zulip,timabbott/zulip,synicalsyntax/zulip,timabbott/zulip,eeshangarg/zulip,hackerkid/zulip,kou/zulip,eeshangarg/zulip,hackerkid/zulip,timabbott/zulip,showell/zulip,zulip/zulip,timabbott/zulip,zulip/zulip