Updates to Codecs' tests
1. Removing VideoBuffer and replacing with VideoFrame.
2. Removing legacy rawImage related code.
Open TODO: Get the frame type, only used in the packet_loss test - a TODO was added.

Review URL: https://webrtc-codereview.appspot.com/896004

git-svn-id: http://webrtc.googlecode.com/svn/trunk/src@2954 4adac7df-926f-26a2-2b94-8c16560cd09d