Reorganize media::VideoCapture* types

The purpose of this CL is to clean up the distinction between
VideoCaptureFormat (which identifies the captured type of a frame),
VideoCaptureParams (which identifies the requested format of a capture),
and VideoCaptureCapability (which identifies the capture capabilities of a
device).

Notably:
* VideoCaptureFormat::frame_size_type ->
  VideoCaptureParams::allow_resolution_change, as variable resolution
  capability is a per-session, not a per-frame property.
* VideoCaptureCapability::color -> VideoCaptureFormat::pixel_format, as frame
  color format is a per-frame property.
  * As VideoCaptureParams holds a VideoCaptureFormat member, capture requests
    are able now to request a particular capture color format.

BUG=269312
TEST=local build, run unittests, chrome on CrOS snow, desktop Linux

Review URL: https://codereview.chromium.org/68503005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236927 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236927