FakeVideoCaptureDevice: Y16 testing support.

Adds:
- support for Y16 buffer format.
- support for defining number of devices from command line.
- generated color control points in corners that could be used to verify the
  frame rendering with no need for the reference render bitmap.

BUG=624436

Review-Url: https://codereview.chromium.org/2447233002
Cr-Commit-Position: refs/heads/master@{#428001}
5 files changed