Reenable GetStats test.

Also increasing start bitrate to have the test go significantly faster
on average. Hopefully an assert hit in the jitter buffer while running
this test was fixed in r7735.

R=stefan@webrtc.org
BUG=4014

Review URL: https://webrtc-codereview.appspot.com/26239004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7744 4adac7df-926f-26a2-2b94-8c16560cd09d