Adding a couple of tests that tries to trigger a certain divide-by-zero issue. The tests triggered the issue, but this CL also includes a fix for this. BUG=3761 R=tina.legrand@webrtc.org Review URL: https://webrtc-codereview.appspot.com/22269004 git-svn-id: http://webrtc.googlecode.com/svn/trunk@7025 4adac7df-926f-26a2-2b94-8c16560cd09d