Backed out 2 changesets (bug 957652) because bug 957431 is being backed out, a=sylvestre

Backed out changeset 92efd61cfca5 (bug 957652)
Backed out changeset 9d405c64a7bf (bug 957652)
 Backed out 2 changesets (bug 957431) because we decided we're keeping Attr.ownerElement in the end; a=sylvestre

Backed out changeset ab12a8416a1d (bug 957431)
Backed out changeset 188d1e255d40 (bug 957431)