webkitpy: Add an explicit ImageDiffResult.passed rather than relying on diff_image being non-None
Created attachment 442409 [details] Patch
Created attachment 442412 [details] Patch
Committed r284845 (243522@main): <https://commits.webkit.org/243522@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 442412 [details].
<rdar://problem/84636930>