Add v4l2capture to support webcam-based speed index in telemetry

v4l2capture is a python C extension to access Video4Linux camera
devices.

BUG=331450

Review URL: https://codereview.chromium.org/123743004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248546 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248546