Merge pull request #18314 from davidflanagan/bug995432

Bug 995432: enable C-AF if the hardware supports it r=jdarcangelo(cherry picked from commit 35ed2ac8d17d373d5e34037bb24e60686561fa84)
Merge pull request #18315 from davidflanagan/bug995432-v1.4

Merge pull request #18314 from davidflanagan/bug995432