Update the output pixel format to the client supplied format when
starting camera capture.
Also add a new API method to get the preferred output pixel format
according to the
AVCaptureVideoDataOutput#availableVideoCVPixelFormatTypes method and
use it in AppRTCMobile.
Bug: webrtc:8505
Change-Id: Ia24eaf91d70d0703a34d38b06bb6eea28fb922b8
Reviewed-on: https://webrtc-review.googlesource.com/22680
Commit-Queue: Anders Carlsson <andersc@webrtc.org>
Reviewed-by: Zeke Chin <tkchin@webrtc.org>
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20697}
