Media Capture Depth Stream Extensions: split videoKind feature.

Split videoKind from MediaCaptureDepth to MediaCaptureDepthVideoKind
feature in order to ship it sooner then the other Media Capture Depth
stream API extensions.

videoKind is important as it enables constraining query (getUserMedia)
to depth stream - see https://codereview.chromium.org/2664673002/

BUG=686756, 616098

Change-Id: I4cca58d763278bbe74d693a2a2ff4b6801a4d126
Reviewed-on: https://chromium-review.googlesource.com/608067
Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Aleksandar Stojiljkovic <aleksandar.stojiljkovic@intel.com>
Cr-Commit-Position: refs/heads/master@{#493711}
6 files changed