Refactor frame generation code so it can be used by multiple modules.

R=pbos@webrtc.org, stefan@webrtc.org, pbos, stefan
BUG=

Review URL: https://webrtc-codereview.appspot.com/2240004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@4791 4adac7df-926f-26a2-2b94-8c16560cd09d
15 files changed