Image Capture: add |supports_torch| field to mojom

This CL adds |supports_torch| to mojom.PhotoCapabilities, to differentiate
the capability from the actual value of |torch|, and wires it
for the Android implementations and for the LayoutTests.

Tested via unittests and manual test using
https://rawgit.com/Miguelao/demos/master/imagecapture.html

BUG=700607

Review-Url: https://codereview.chromium.org/2798263003
Cr-Commit-Position: refs/heads/master@{#462731}
14 files changed