Add VideoCaptureFactory so that we don't need to expose VideoCaptureImpl.

BUG=
TEST=

Review URL: http://webrtc-codereview.appspot.com/213002

git-svn-id: http://webrtc.googlecode.com/svn/trunk@727 4adac7df-926f-26a2-2b94-8c16560cd09d
14 files changed