Merge pull request #18249 from davidflanagan/bug995432

Bug 995432: simple continuous auto focus support r=jdarcangelo(cherry picked from commit 289f131cc65dbf35f69924254a71e76628d2e36d)
Merge pull request #18306 from davidflanagan/bug995432-v1.4

Merge pull request #18249 from davidflanagan/bug995432