Fix color format mapping for RGB24.

The color format media::PIXEL_FORMAT_RGB24 should be mapped to libyuv::FOURCC_24BG in VideoCaptureController.

BUG=330839
R=fbarchard@chromium.org

Review URL: https://codereview.chromium.org/118123003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242650 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242650