If you do an erase install or blow away your Web Inspector settings, the Canvas Tab is not enabled by default. I think it should be enabled by default, at least while tabs are easy to dismiss.
<rdar://problem/35938917>
Created attachment 329458 [details] Patch
Comment on attachment 329458 [details] Patch r=me
Comment on attachment 329458 [details] Patch Clearing flags on attachment: 329458 Committed r225979: <https://trac.webkit.org/changeset/225979>
All reviewed patches have been landed. Closing bug.