For the legacy protocol supported by safaridriver, people expect a screenshot of the entire contents, not the viewport. And there is no workaround because Element Screenshot is not supported by the driver. Instead, add a legacy behavior flag. This can be removed when safaridriver only needs to support W3C protocol.
<rdar://problem/34379930>
Created attachment 328385 [details] Patch
Comment on attachment 328385 [details] Patch r=me
Comment on attachment 328385 [details] Patch Clearing flags on attachment: 328385 Committed r225501: <https://trac.webkit.org/changeset/225501>
All reviewed patches have been landed. Closing bug.